Whenever I have to start windows 10, I still see the same kind of bugs, that were present on XP. One example: They seem to be simply unable to fix the icons "near the clock", which are still shown, when some app has been killed, until you hover over them. Things like that, but of course also lots of stuff that affects people more in form of annoyances, making every action take at least twice as long as on GNU/Linux distros I run. It only takes minutes, and I am already frustrated with the system, because everything takes so long to do.
One similarly ignored bug that springs to mind is the performance of the "Send To" context menu item in File Explorer. I always dreaded dragging my mouse over it by accident.
They could also cache that computed menu and proactively update the cache whenever the relevant keys are changed. Either way, pretty far from "cannot be fixed without breaking the API".
