Hey,
We've just migrated a 3.5 application to Qooxdoo 4.0 and we've found a behavior change in selections that affects the way interaction occurs in that application.

In 3.5, both in trees and tables (and everywhere I suppose), the selection of the item is done in the MouseDown event while in 4.0 is done when the Mouse button is released (MouseUp / PointerUp or Click / Tap). I've seen that handleMouseDown() and handleMouseUp() methods in the manager class have been replaced by a single handleTap() method, but I still do not find the way to get it working like it did in 3.5 (I got it partially, but then multi-selections got broken).

PS: I've applied the patch (bug #8434), that was the only related bug I could find.

You can just view what I am talking about in the showcase:

Qooxdoo 3.5.1

http://demo.qooxdoo.org/3.5.1/showcase/#Table
http://demo.qooxdoo.org/3.5.1/showcase/#Tree

Qooxdoo 4.0

http://demo.qooxdoo.org/current/showcase/#Table
http://demo.qooxdoo.org/current/showcase/#Tree

That behavior change was necessary due to the touch support. Scrolling on a touch device starts with a touch on the item followed by a swipe. If the widgets change the selection on the first interaction e.g. mousedown / pointerdown the selection would also change on a touch scroll which is an unexpected behavior. So this change was necessary and on intension. :)
Do you still having problems updating your code? If so, what are the issues?

Regards,
Martin