If you downloaded the beta very soon after release, it might be this bug:
Check your build number, if it's 9465 you should re-download and see if it fixes those issues.
We had a crash from this just the other day
Just because it doesn't happen all the time doesn't mean it can't happen. The fact remains is it's fundementally unsafe - jscript objects aren't meant to outlive the instance of the script engine that created them.