Trying to insert text into a Razor document during Razor integration tests results in an error in razorDocumentSynchronizer.

So far I've seen it only in Razor integraiton tests and I haven't been able to figure out the exact root cause as the issue is intermittent and not easy to hit under debugger.

Incidentally it was failing our Razor integration completion tests since they were the only ones modifying the document. I removed document modification from those tests for now to make them reliable and filing this separate issue to investigate further.