I noticed when setting permissions for the Forum by Usergroups using the Permissions Tree Editor, if I set a permission for one usergroup and use the repeat for other Usergroups feature… it works as expected by the little instruction given - but then if I try to change one of the usergroups after that I am not able to… UNLESS I set the permissions and move out of that forum and on to another task - THEN return to the particular forum I was working on before and THEN it seems I am able to revise or change the permission for a usergroup (that previously was impossible). don't know if this is a bug or just an oddity to deal with but the end of it all was I was able to workaround he quirk and set my permissions the way I intended to at first.

I think what is happening, is you need to click the copy button again to stop copying mode, but due to a bug it's not blinking like the message says it should be.
Hot fix:
0004516: Blink effect in Permission Tree Editor not working - Composr CMS feature tracker