Interesting question. This trigger is one I usually use on a field where exiting the field after changing the value to something new trips this trigger.
In my own "quickie test", I cannot trip this trigger for a popover button or the popover panel even though it as listed as a script trigger for both. My tests were not exhaustive, so someone else may chime in and correct me, but as far as I can determine, this is not a trigger you can use with a popover button or the panel that it opens. The OnObjectEnter and the OnObjectExit triggers, on the other hand, can be used with a popover.