I stumbled over a few bugs in WPF (worked in WPF3.5, would hang in WPF4), which were, for at least 4 years, documented and "WONTFIX" with no acceptable workaround (workaround provided slows things down by a factor of 10 under some circumstances).

Maybe it's fixed with the reinvigorated WPF on Win10. I don't care anymore, but I do caution anyone to ever use any MS Technology younger than 15 years.