Only syncs when power cable attached

Not sure if this is a bug or a feature, but either way it's a pain.

the aCalDAV account on my phone only syncs (either aito sync or with the Sync now button) when the power cable on my phone is plugged in. Refuses to run on battery, but doesn't error or even seem to attempt it.

None of my other accounts for other things do this, and cannot spot any settings o my phone to dictate this, so I'm guessing it's an issue with aCalDAV itself.