indeed, my jvc does a similar thing. with a battery attached its a handy function as if you're not using the camera (or what it thinks as not being used) then you wont drain it, but if you've got the adapter attached.... why!
Leaving the cassette door open or not putting a cassette in will prevent the camera from going into standby. This feature is to prevent head damage when there is a tape in the drive.
I wanted to prevent the camera entering standby when there is a tape in the camera and when it is not recording i.e. turn off the heads.
Is there a hidden feature that will allow you to do this?
Daft question, but if you don't want to record, why do you need to have a tape present ?
Seems that the lack of need for a tape would result in no tape being present, which would result in standby mode not being activated, and so solving your problem ?