Steps to reproduce

1.  Create a page with a dialog containing a rich text field
2.  Open Resources App. Create a file containing Javascript for a custom rich text field. You can copy the default JS found in config-magnolia.js
3.  Include some item that requires a dropdown on the toolbar. Example : you can add "Format" to the list within the JS:

   { name: "styles",        items: [ "Font", "FontSize", "TextColor" ] },

1. Enable the old pages app by removing the "pages" node from ui-admincentral/config/appLauncherLayout/hiddenApps
2. Edit the page with the rich text field and try to click on a dropdown from the toolbar within the field

Expected results

 You can click on the dropdown and see its options

Actual results

Nothing happens when you click on the dropdown

Development notes

This is reproduceable on the demo. This is happening for the old version of the Pages App. Strangely enough, if you put an incorrect path to the JS, the page seems to default to another config.js and the dropdowns work for that default file it brings up. But not the custom one.