This problem was pointed out on the [[https://de.wikipedia.org/w/index.php?title=Wikipedia:Technik/Text/Edit/VisualEditor/R%C3%BCckmeldungen&oldid=178520927#Bearbeitung_nicht_m%C3%B6glich|German-language Wikipedia's feedback page yesterday]]. ~~It might be related to the second problem in {T145268}.~~
When you
# go to a category page, e.g. [[ https://de.wikipedia.org/wiki/Kategorie:Hunde | Kategorie:Hunde ]]
# click //edit// to enter the visual editing mode
you see the content of the category at the bottom: {F22482284}
However, when you
# go to a category page, e.g. [[ https://de.wikipedia.org/wiki/Kategorie:Hunde | Kategorie:Hunde ]]
# click //edit source// to enter the source code editing mode
# click on the pen in the upper right-hand corner of the editor to switch to visual editing
there is no category content shown: {F22482293}
One would expect to see the same listing of pages as when directly opening the page in the VisualEditor.
If one first opens the page in visual editing mode, then switches to source code editing, and then switches back, no category content is shown either.