A recent Gmail update crashes Mailplane, Safari, and other WebKit based applications. The Gmail help forum has a couple of threads concerning this problem and it is now listed on the Gmail known issues page. Not all Gmail accounts seem to be affected, but those who are, experience a duplicating chat box that lead to a crash.
Solution: If you affected by this Gmail bug, consider using the 2.1.3 preview version. It contains the latest WebKit nightly build, which solves the issue.