Hi,
I encountered a behavior which perhaps might be considered a bug - exp_category_posts table not updated when one would expect it to be updated.
Let me describe an example of such behavior.
Say you have a category which has category id 260. Then you post into that category an entry, which has entry id 3377. Then if you run the code
{exp:query sql="SELECT cat_id FROM exp_category_posts WHERE entry_id = '3377'"}
{cat_id}
{/exp:query}
the category id of the entry will be displayed.
Now say you create a category which has category id 261 and after that you make this category the parent of the category 260.
Having made such changes you would expect that the code above will display both category ids - 260 and 261. But instead it will display only 260 as earlier.
Both category ids will be displayed only in case the entry 3377 will be updated after category 261 was made the parent of the category 260.
It seems to me that such behavior is not good; it seems that after some category was made a parent of some other category, the table exp_category_posts should be updated accordingly to reflect the change.