To reproduce, Vaadin has to be in debug mode, then enable a tool like Firebug on the client side.

When opening an app and clicking on a tab (e. g. use the contacts app), a multitude of errors are displayed in the error console (on the client side only). There is no logging on the server side regarding those errors.

Example (Firebug stops error display because there are too many)

Mon Apr 25 11:56:10 GMT+200 2016 com.vaadin.client.ApplicationConfiguration
SEVERE: Exception caught: Exception caught: Exception caught: Can't get element 0com.google.gwt.event.shared.UmbrellaException: Exception caught: Exception caught: Exception caught: Can't get element 0
at Unknown.Ac(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ps(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.us(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.yy(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ny(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.be(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.sra(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.RD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ee(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.VB(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ZC(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Yp/<(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.anonymous(Unknown)
Caused by: com.google.web.bindery.event.shared.UmbrellaException: Exception caught: Exception caught: Can't get element 0
at Unknown.Ac(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ps(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.us(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.yy(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.upb(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ed(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.be(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.sra(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.RD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ee(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.VB(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ZC(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Yp/<(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.anonymous(Unknown)
Caused by: com.google.gwt.event.shared.UmbrellaException: Exception caught: Can't get element 0
at Unknown.Ac(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ps(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.us(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.yy(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ny(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Do(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.upb(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ed(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.be(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.sra(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.RD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ee(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.VB(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ZC(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Yp/<(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.anonymous(Unknown)
Caused by: java.lang.IndexOutOfBoundsException: Can't get element 0
at Unknown.Ac(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ps(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.vs(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.vt(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.R1(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown._q(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ckb(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Do(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Do(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.upb(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ed(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.wd(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ud(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.my(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ey(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.PD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.be(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.sra(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.RD(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Ee(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.VB(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.ZC(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.Yp/<(info.magnolia.widgetset.MagnoliaWidgetSet-0.js)
at Unknown.anonymous(Unknown)

info.magnolia.widgetset.MagnoliaWidgetSet-0.js
Line 304