Curious question about AutoCompress after opening P4 Vista VM

I thought I should mention that I think I've found a bug, it may or may not be but:
I opened my Vista VM after installing Parallels Tools I opened the configuration section and clicked OK and it prompted me and said AutoCompress cannot be used with Undo Disks, however I don't think I touched any settings.

So I thought perhaps when upgrading and Undo Disks is turned on AutoCompress is on too, I thought that may cause problems? I don't know.
I turned mine off just to be safe.

Kind Regards