Can I back up multiple volumes using Time Machine on Snow Leopard?

I have a fault with my time machine software where it is no longer able to perform incremental back ups of the volumes (partitions) I have created on my internal hard drive - every attempt results in a full back up. However incremental back up of the Mac HD is working. I have had it working perfectly in the past. I'm backing up to a dedicated external hard drive.

I have just been told by an apple support manager that Time machine on OS 10.6.8 is not designed to back up multiple volumes (partitions) on my internal hard drive, only the current Mac HD drive - is this correct? He said it shouldn't be backing up the other volumes and the reason it is doing so and has done so in the past is because of bug!

Surely this is not the case?