unexpected rm error

[Junior <ejr@inbox.com>]

I have a filesystem mounted on /tmp which is on system ram.
When I do a "rm -fr ./*" I get the following message:
 
rm: unable to remove `/tmp/usr/include/linux': Directory not empty
rm: unable to remove `/tmp/usr/include': Directory not empty
rm: unable to remove `/tmp/usr': Directory not empty
rm: unable to remove `/tmp': Directory not empty

I normally do it twice to delete everything but it always bother
me why I get this message in the first place. I am at root with the appropriate permisions
so I shouldn't be getting any errors. Why not the other directories?

Does anyone have an answer to this?

Thanks.
-Jr.