It has been discussed recently in two distinct scrapbooking forums.
- it's very easy to drag a category over another one, changing it to a subcategory in the keywords panel.
- The solution was before to use the 'edit' menu choice for the subcategory and to choose the parent category as 'None - change to a category'. Unfortunately that no longer works.
I have no idea why the bug has never been corrected since that time; there may be some technical issue but in that case, the suggested solution should not been kept.
The workaround I have given is:
My workkaround tested with my Food category: - I created a new category with a similar name (Foods instead of food) - I selected all the keywords in the Food subcategory by highlighting the names, not the checkboxes; then dragged them into Foods - Same for the subcategories of food. You can shift click to select all then drag. After checking that Food was empty, I deleted it.
I highly recommend to work on a catalog folder copy for safety."
I'll report this also in the feedback forum, where you can add your vote if you are concerned by that bug.