Dear Klaus,
I understand this is quite an old thread, but I'm kind of experiencing this same issue now with version 1.18.
Instead of changing urls, it seems to be an issue of changing the crop. I have a few png buttons, which change their cropping when clicked, and also have a showtext call attached to their onhover events. Now normally it works just fine, but if I click the button and move the mouse away fast, the label sticks to the mouse cursor and I can't make it disappear until I hover over the button again (and then move the mouse away).
I'm using the HTML5 version.
Can you confirm this bug? Is there any workaround, so that I don't have to wait for the next release or the one after that for a fix? Thanks!