After some testings...
As a workaround, until development team solves it:
If you rightclick on the group you can copy the link to the group you want to remove
Now open a new tab in the browser, paste the link **before hitting enter** change the "a=edit" in the link to "a=delete"
Now you will get an errorpage, but if you look bit down in the text you can actually see that the group was removed
After this you can close this extra tab in the browser
One funny thing: If you now click on the group you just deleted, you will get information that the group does not exists, and then (in my case) you will see the old Group managing page...
I guess there is some kind of link/setting that is wrong in the new FO 3.x
