Since 20/4/15 I have had three users experiencing the same visual glitches when using Excel. Images from windows which are behind the active Excel window show through the active Excel window - see http://i.imgur.com/sl5yU3p.png
Other images show through the window too (not just desktop icons), such as open PDF files, windows explorer items etc.
One user reported experiencing the problem when using their roaming profile through a VPN.
I have rebooted the users' machines, turned off Windows animations, reinstalled graphics drivers, ran a repair on Office and disabled visual themes as well as desktop composition under Excel's compatibility settings. None of these fixes have resolved the issues.
Please advise as to possible solutions.