Although this Thread is already very old, I want to share my experiences anyway.
First of all thank you Deb for the good explanation of this error!
We got also the mentioned error message in the logs and after reading your post I understood why.
We also have several iRules assigned to the affected VS, one of them doing a redirect. The header insert was in a separate iRule at the end of the iRules list. So I moved this iRule to the first position and now the error doesn't occur anymore.
So your "event disable all" is not required for us.
Ciao Stefan :)