Save, Save & Close buttons in Ribbon Bar not working

I have a strange issue happening with a couple of my end-users.  Sometimes when they launch a new CRM Form window the Save, Save & Close and other buttons on the Ribbon are appear not to be working.  They are using IE 11, and we have CRM 2011 v.  They are NOT greyed-out or anything, but when you hover your mouse over them they do not "highlight" like they normally do.  Could this be a PC/Resource issue like not enough RAM?  They currently have 4GB.  I cannot find this issue anywhere else on the forums.