[userbinator]

The reason could be stated in one word: "architecture", or perhaps less positively, "bureaucracy". In other words, either they could've designed it originally in such a way as to make fixing such a bug very difficult to do without rewriting massive amounts of code, or the fix could be simple yet the politics around actually getting that fix into code are not.

Having worked at large corporations (not Microsoft) before, I can definitely see how things like this happen --- and the reason why "enterprise" software tends to have a lot of these superficially simple and annoying defects. To add insult to injury, the codebase is often offensively overengineered and in precisely the wrong direction to facilitate the change required to fix such bugs, and even the tiniest of changes requires a ton of extra paperwork, approvals, and reviews.

[gambiting]

Vista and 7 had a well known bug where a contextual window would stay on screen forever, until you changed the resolution or logged out - I think Microsoft commented on this officially, saying that fixing it would need to be done somewhere low at the kernel level and it's simply too much work. I think it was resolved fully in 10.