after editing the weblog settings, the tab "subweblogs" becomes empty (there are only the two buttons: save and back).
not only this, the weblog listing page (index.php?page=weblogs) then stops showing the assigned categories.
this happens when there is more than one weblog present.
I am not able to further track it down.
it seems that previously assigned categories are still working (well, i'm not entirely sure about it), but they are not displayed or editable anymore.
this is a pain in the ass: you have to delete the weblog and enter everything again. if you miss something and want to re-edit any (i guess any) of the weblog settings you'll lose the posibility to edit the categories in the subweblog tab. well you could try and edit the ser_weblogs.php file but then you'll have to count characters (its an awful format, sorry, am ranting

couldn't you change those configs to use json or xml?
thanx
EDIT: this happens when opening the editing page of a weblog, you don't need to save anything and the categories get removed.