Like I said, bugs reported from customers get a higher priority, doesn't mean they will get fixed within x amount of days. Let's be honest, everything has bugs in it, it's the nature of software. I'm not saying this is acceptable but if given a proper test case bugs can get fixed quickly, I've seen this happen numerous times. Part of bugs are regressions, things that were fixed may break in new versions. Watching the Ext JS team get through the bugs as fast as they have is tremendous, 4.2.1 is going to have a ton of fixes. I personally updated a couple of my apps to 4.2.0 and experienced to api changes or bugs. In my experience, 4.2.0 has been a very solid and performant release but mileage will always very.
As for support for "long term support", we support all versions for a long time, Ext JS 3.4 has been out for years and is still supported. If feasible, workarounds will be given for any version.
We all agree that any software has bugs. However, Sencha did not get the point that some bugs will make a product unusable (unstable), these bugs should be fixed right way or give a work around. That what we paid for the premium support.
Extjs 4.x.x was released more than two years ago, however, all released versions 4.0.x, 4.1.x and 4.2.x have critical bugs.