This is best explained in practice by the reduction that follows.
This has been occurring only in the most recent nightly builds (currently running revision 21682)
Created attachment 14705 [details]
Reduced testcase for this bug
Test case contains basic instructions for reproducing bug
Created attachment 14706 [details]
Updated m_lastOnChangeIndex before dispatching the change event to avoid reentrancy
Landed in r21734.
Fixed in ten hours!?!?! Are you guys trying to break some kind of speed record?