Over the past several months, I've spent some time fixing lots of jQuery event bugs related to Internet Explorer 6, 7, and 8 in preparation for the upcoming jQuery 1.7 release. Most of these were jQuery bugs in the sense that we didn't put enough extra lipstick on the pig to make it seem as attractive and standards-compatible as modern browsers. One phenomenon that interested me about these bugs was that they had all been reported in the past 18 months, but had been in jQuery for several years. So if that is the case, why were they just being reported now? I have a theory.
If you were a web developer five years ago, you had to really know the quirks and inconsistencies of the major browsers of the day, primarily Internet Explorer 6/7, Firefox 2/3, and Safari 2/3. Libraries like jQuery were created to help developers deal with those problems, but nearly all developers were well aware of the issues that were being normalized within the library. That usually meant their own battle scars prevented them from going into territories where they'd been burned before, so jQuery's valiant-yet-imperfect attempts to fix IE were good enough in most cases.
As the older IEs become less mainstream yet still important, it's probable that IE-related jQuery bugs will continue to come in as developers discover more ways that their standards-based hopes are dashed. If it's feasible we'll fix them, but that doesn't excuse any web developer from having a basic understanding of the quirks and pitfalls of IE. There will always be things that jQuery can't fix--eventually we're going to run out of lipstick.
The good news is that the rewritten IE event support in jQuery 1.7 closed many bugs and actually reduced the size of that code by nearly half, so the world is paying a much lower price for it. Only time will tell if that code meets the expectations of developers who expect strict standards compliance, even from browsers released in 2001.