Permission denied on files from same group.

Hello,
I'd like to report something, that I consider a bug.
I'll describe the situation:
folder: www, group/owner = apache:apache
user: howit group: apache (same as the owner of the file)
file settings: apache:apache chmod : 664 (group editable)
when I log in as normal user (either sftp or scp), i cannot edit or rename other files then these created by myself, even being in the same group.

A workaround was disabling the preserve timestamp under transfer settings. but i still cannot rename them.

Suggestions? is this a bug? why?

thanks everyone.

AFAIK, you need to have write permissions to the containing directory to be able to rename files.