Engine: Screen goes black when switching from Polymer to Classic after having seen a mirror

Very similar to Issue #49 (closed), but does not stem from the same commit. I do believe they are related however.

Example map: polymer_mirror_bug.map

Steps to reproduce:

1. Start the map in Polymer.
2. Turn away from the mirror such that it is no longer in view.
3. While the mirror is out of view, switch to Classic.
4. The screen will now be entirely black, but the game remains controllable.

Additional Information:

This happens any time the player has previously seen a mirror in the Polymer renderer.

Looking at the mirror again or switching to Polymer turns everything back to normal.

This started occurring with SVN commit r7733 (commit: 5bc0157d). Perhaps investigating Issue #49 (closed) can also help resolve this problem.