Nested group file permissions not taking effect

Alright, here was my problem. I have a 2008r2 file server, tons of files, and we are removing everyone's full access rights and doing 3 groups for each root folder, a full control, modify and read only. We ran into a problem where if you put a user in one of the groups to give them access, they still would not have access. The fix, sort of simple, but dumb. For us, a simple log off and log on of the user didn't fix it. We had to go in after they tried, using computer management, close their connected files and sessions, have the user log off, then log back on. And poof it worked.