Last week, I released a new version of eLAS, a PHP based web application. This version included a combination of changes in 2 branches., trunk and an experimental branch that introduced the Mootools javascript framework. Both branches received significant testing and worked and behaved well.
The merge with the Mootools branch happened very late in the 2.2 cycle because version 3 (which would have gotten this) will not happen for at least another year.
So, after merging in the Mootools branch, I tested it in full using my own (Linux) laptop and it worked great.
The upgrade on all sites went extremeley smooth, but user reports of failures started coming in hours later. They all related to IE (only version 8 confirmed).
Apparently, IE8 cannot handle the combination of the new Mootools AJAX calls and the legacy javascript that did XMLHttpRequets. All other browsers can (as per usual).
So, for the next releases, I'll make sure I get to test the horrific IE browser much deeper and avoid last-minute merges, no matter how well tested they where separately... And now on to two bugfix releases to get this behind me...