Hey,
this is quite strange and never happened for me.
Maybe something in the packaging code (i think updating from 10.5.0-1 to 10.5.0-4 isn’t doing an ownCloud update and only reflects a code change in the packaging) has triggered this behavior?
Thanks for providing the insights on the category topic, i have created Change order of available categories when creating a new topic? about that and hope that the ownCloud people are able to do something about this.