Ok, I figured I would try to reproduce the same results with a second webserver by installing roundcube in a vhost. So here is a seperate server never having email, no plugins etc. RoundCube freezes when your in the "Settings" and you click between the three tabs too quickly.
Now I'm starting to think that this is a bug of some sort in the roundcube app because I've checked all my webmail clients on all webservers and their all doing the same thing in roundcube.
However I only have one ISPConfig3 server and it does not have the 403 error it just freezes period and after a minute or so it will let you click again.
I know some one is thinking "this guy must be a clicker
" but seriously it's weird I was just jamin through my setups adding domains and email and bam my panel froze on me and it's very reproduceable it's not hard to make it freeze. So I don't know if it's somthing with just my setup or what. Come to think about it my old roundcube setup froze allot as well even when trying to compose an email it would just freeze so I'm really leaning tword bug here.