Jesse – I have not been able to reproduce with TextEdit, but I think it is related to the speed of the updates (depending on the settings, nvUltra can attempt to update the file as quickly as every keystroke).
It was the speed which served as a stress test in my own development that revealed the issue in my own code. Less frequent saves passed through unscathed, so I did not initially detect the flaws in my own file writing/reading threading early on.
Email me and I can get you a link for nvUltra beta that should make it trivial to reproduce this so you can see whether there is a threading issue in TaskPaper. That is probably the easiest way to demonstrate this.