Firing at the windows of houses from within will result in the window breaking, however the following projectiles will continue to hit and be deflected by a window material. The window breaks, but the rounds keep hitting invisible glass where the window used to be. Only tested on white two story buildings.
The bug is fixed when you leave the building and re-enter it.
19/11/2015
On stable branch this affects about half of the windows.
02/12/2015