Scrollable tooltips are the coolest feature in IDEA since Ctrl-Click (for me). Unfortunately they don't work properly on Mac OS X. Hovering the mouse over a large string pops up the tooltip pane with a scrollbar, but any movement will cause the tooltip to disappear. Hence you can't scroll. I'm going to guess at what is going wrong here. I think perhaps the popup is one-pixel away from the mouse cursor's hotspot. And that the very first movement of the mouse cursor fails the "isCursorInsideTooltip" test. Perhaps place that popup at (currentX -1, currentY - 1) and maybe that will fix the problem?