In HTML5 only, click boxes with overlapping hint shapes flicker with mouse movement

Has anyone run into an issue where, in HTML5 only, if they've got a hint box that overlaps a click box, moving the mouse over the click area causes a rapid flickering between the hint overlay and the clickable area? It makes it a struggle to click the item, forcing you to rapidly click multiple times to actually register a click properly, and it looks pretty bad as well.

Any ideas on this? I use hint boxes often as "bounding boxes" or an "overshadow" for the clickable area, and in flash it worked great, but now as we're trying to move to HTML5, we've been running into this issue frequently.