FAQ47 should be updated. Indeed in order to delete tag from entry in memories you need to delete it from both the text box with comma-delimited list and from and from the list below.
The following text was suggested:
Editing or deleting the category keyword on all memories associated with that category. In order to delete a category keyword on a memory, you must both remove it from the comma-delimited list of keywords and unselect it from the box of keywords below that before clicking Submit. In order to edit a keyword (such as to fix a spelling error or to replace one keyword on a memory with another), you must edit the keyword in the comma-delimited list of keywords and unselect the old keyword from the box of keywords before clicking Submit.