I was still seeing a high prevalence of such issues, albeit sporadic and indeterminate with RU5 - mostly in our development environment, where I can have open (open and closed repeatedly within the one IE process) many different CRM Orgs at any one time.
Both our dev and hosted production environments are now on RU6 - while it doesn't appear to have been as obvious thus far, it is still too soon to tell as we only applied the updates over the weekend.
--pogo (pat) @ pogo69.wordpress.com