I found a qt webkit bug
if on windows 7 computer, and the audio driver had been installed with windows' driver, then use webkit play a html file which contain three or more Audio tag, the it will be hung up.
if the audio driver reinstall with the hardware's driver, it has no the problem.
Search for your issues here: https://bugreports.qt-project.org/secure/BrowseProjects.jspa
If you are sure, the bug exists ans was not fixes till today, create a new one.