Just incase anyone else runs into this and Googles.
If you have a flash movie which mysteriously seems to reload itself during some fairly innocuous and un-connected Javascript execution - take note:
Dynamically setting document.body.style.background was the culprit for us. Don’t ask how I managed to identify this as the culprit, suffice to say it involved a lot of logging statements and patience. Doing this immediately caused the flash movie to reload itself, causing havoc in our case as we use it to play music and connect to a socket server.
You may find, like us, that setting separate background properties, eg document.body.style.backgroundImage, worked around the issue.
Anyone hazard a guess as to why the Flash runtime feels the need to implement this behaviour? Perhaps something related to wmode=transparent? (although we’re not using it)