When I was using Windows 98 back in the day, I noticed a bug in the taskbar: it would randomly refuse to auto-hide, even though I had auto-hide enabled. When I eventually upgraded to Windows XP, I noticed a taskbar bug that prevented it from auto-hiding. In Windows, Vista, guess what I noticed. And Seven. And the release candidate for Windows 8 (I've never used the actual release of 8). Assuming it hasn't been fixed in 10 (if it hasn't, that's the least of 10's issues) it's taking Microsoft almost two decades to fix this simple bug. In the meantime, it almost seems like Microsoft is hell-bent on making as many new bugs as it can.
Perhaps it's because there's just too much code to be maintained. I've been saying this for far too long: Microsoft needs to slim down Windows. It should NEVER have reached the point where the OS itself takes 16GB+ of storage for the original installation (plus updates, drivers, more updates, etc.). This might sound crazy, but I think a lot of users would prefer that space be used by (gasp!) actual programs, or perhaps things like documents, movies, music, etc.
If I were Microsoft in the 1990s, my main direction would have been to modularize the heck out of the system, so that future updates/improvements can be implemented by only adding/removing/modifying specific modules. Instead, Microsoft seems to have insisted on piling new code on old code, just to bury that under newer code, which gets buried under newer code, etc. So each new feature consists of a million old features carelessly thrown on top of eachother, the eventual result being the collapse of the entire tower. And when that happened, Microsoft proudly called it "Windows 10", presumably because no one taught Bill Gates how to count.