Logging onto WOTLK and Cata at same time ...

is there any rule against being logged onto both WOTLK and Cata at the same time with the same account? I did it by accident tonight- thought I'd closed my Cata client but it was just minimized. I was surprised it didn't log me off and that I was allowed to be on both at once.

Then it occurred to me that this could be useful- I could be waiting for a spirit beast on my Cata hunter while herbing on my WOTLK druid.

So I'd like to do it on purpose from time to time, just want to make sure it isn't against the rules.

Please clarify whether it is ok or not.

There should be no issues with this, as long as you are not using a bot of some sort to avoid the anti-afk kick mechanism (servers kick players after an extensive period of inactivity). In retail terms, it would be equivalent to camping your spirit beast in WoW, and playing another game on your computer at the same time.

A GM should confirm this too.