Plone version 4.3.2:
boom, Tinymce disappears...
now, in the jsregistry.xml there are the following two lines:
The first one, I have no clue what it is supposed to do. If you disable it, everything works again. Both Plomino and Collective.cover, also with RichText Tiles.
UPDATE: it appears this has been noticed before in #213 , but now it is actively harmful to have it included.
Some more (manual) testing reveals:
Remove tinyMCE bundle overrides, that was causing the issue #303.
Move upgrade step for issue #303 to version 6.