I tried to save an new User I had created in the security app. The validation came up with an error due to having added a space at the end of the email address. When I klicked on "jump to next error" in the validation message the following error was thrown:
Unable to invoke method focusNextProblematicField in info.magnolia.ui.vaadin.gwt.client.form.rpc.FormServerRpc
caused by InvocationTargetException
caused by NullPointerException

I was locked in as superuser. I tried to reproduce the error and apparently it only comes up, when you are trying to do this having all Tabs displayed as one "Show all". If I do it from inside one dedicated tab, eg. "user info" the NullPointerException doesn´t show up.