Windows have black borders after hibernation Unity
This is a known bug in Ubuntu 14.04 => https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/1292830, please vote for it by clicking the green text at the top of the page that says "This bug affects 69 people, but not you".
A temporary workaround is to go into a system terminal mode, careful with this as you need to know how to get back to the Unity desktop otherwise you will have to restart.
- Press Ctrl + Alt + F6 (takes you to system terminal mode)
- Press Ctrl + Alt + F7 (takes you back to the Unity desktop)
Answered by OP in comments.
Seems like I messed up my compiz configuration when upgrading to 14.04. Thanks to user164089 and this post, I tried resetting my compiz settings and it works.
Kudos noleti - I wouldn't have found that answer otherwise.