geom_label: gpt/labelname for gmirror provider?

Hello,

first of all thank you very much for the gpt label support in 
geom_label! This is really nice and makes disk partitioning well-arranged.

I tried to use the gbt/label as provider gor glabel, but that didn't 
work. It looked as if gmirror wrote the label succesfully, but `gmirror 
list` was empty. Just replacing gpt/label with ad4p2 worked as expected.
Is it impossible by design to use gpt/label as provider?

Thanks,

-Harry

P.S. Can I disable ufsid/UFSID and gptid/GPTID? I don't think I'll ever 
use them since I create my own labels on both, GPs and UFSs. A sysctl or 
loader tunable whould be fine.