Steps to reproduce:
- open a large pdf document (my example has 250 pages, using kami pro)
- drag the right-hand scroll slider down to the end of the document
- release and move the mouse elsewhere on the page, click somewhere
- go back and try to drag the right-hand scroll slider back up to somewhere else in the document
- notice that the mouse is NO LONGER ABLE TO SELECT the slider or move it by dragging
- verify that the mouse scroll wheel still works (it should)
If you are very good with the mouse, you will be able to regain drag control over the slider if you grab it by the very bottom edge. Then the slider will turn from gray to black, and be draggable again. Most of the area of the slider rectangle is now "dead" meaning that it does not sense it when the mouse is over that region. In fact, the dead region of the slider rectangle depends on where you are in the document. If you are 60% down inside the document, the top 60% of the slider is dead, etc.