It looks like this is due to the CSS alignment for single-line events (multi-day events seem to fit on a single line), so it was missed in testing on the Full view.
Events with times take up two lines, so the hover box overlaps the event element, and the hover works properly. The scenario you’re running into is happening because there’s a gap between the event in the calendar and its hover box, so the mouse loses the hover state before it gets to the box.
I’ll adjust the CSS placement of the hover boxes so this doesn’t happen. I should be able to release this fix later today, so watch your site admin for an available update.