When grabbing a scrollbar handle in an AE2 GUI, the scrollbar will not take the relative position of the mouse to the scrollbar handle into account, and reposition the scrollbar handle so that it's upper edge is where the mouse cursor is.

This can be observed by pressing (and holding) on the bottom part of the scrollbar handle:

It will reposition immediately to where the cursor is:

It's also possible that the handle is not even considered when clicking, but this should be fixed.