User can't have two functions open.

We have a situation where the user can't have two functions open.  For example, if he has material workbench open and minimized and opens material transactions, then material workbench closes. The user states this "only having one screen opened at a time" started a couple of weeks ago.  Has anyone encounter something like this before?  If so, how can we can we fix it.  I have searched and I can't find anything on this.  Any help will be appreciated.  Thanks!