v2.2.1

Band-aid Fix for BoundingBox cache

In certain circumstances, it appears bounding boxes weren't being stored correctly in the object used to remember prior positions. While I'd like to properly hunt down the bug in the future, for now I'm releasing a "quick fix" that solves the problem by supplying a default, placeholder box when none is found.

This solution appears to work, but this is addressing the symptom, not the cause. Better fix to come!