Yup, i work on software with a Qt GUI and it took us ages to figure out why our daemon (no Qt dependencies) would experience latency when the GUI was open.
For Windows users we now put this var in to global environment via our installer, and probably break other software in the process.
https://bugreports.qt.io/browse/QTBUG-40332
There is a workaround, but developers have to know about it first. And it's such an unexpected and weird behaviour that 99% of developers don't.
This was our fix (1 line of code), in case that helps anyone:
https://github.com/sqlitebrowser/sqlitebrowser/commit/739464...