Nothing should ever crash the interpreter :-)  So this is a thoroughly legitimate bug report.

However, there's no way to guess whether _this_ crasher is easy to fix, or next to impossible.  Without a test program to provoke the error, there's little to go on.  If it were a common problem with daemon threads, I'd expect at least several reports of similar behavior over the decades.  So chances seem to favor that there's something unique about the specifics of what your daemon threads were doing to provoke it - and/or timing quirks specific to your platform.