How to reproduce:
Open any project, go to File, then Export project, select HTML5 website (I have tried that one, as well as the WiiU exporter only), then click Next, and then Next again.
At this point, you can either click "Export" or press "Enter"... immediately after this screen closes, press "Enter". The progress bar for exporting disappears, and nothing is visible... which makes the program appear to hang. Sometimes the export finishes, but sometimes it stays in an infinite loop. (I left it over night once... on an export that usually takes 20-30 seconds)
This is bad for many reasons... sometimes when you export, you just want to go to the next steps fast by pressing enter 5 or 6 times to get through the steps... but if you press enter too many times... you have to pray that it exports fine. I'm sure this is an easy fix... I'm guessing it has something to do with the events in the progress bar window that comes up.
PS. Happens on at least as far back as r159 till the latest beta