How does stitching decide which one to move?

I have two faces UV mapped. Let’s call them P and Q. P is in the right place. I want to attach Q to it.

I select Q and press “V” and Return to stitch them together. It moves P.

Okay, I guess I should do it the other way around, so I select P instead, and press “V”. It moves P again.

What do I do to make it leave P in place and move Q instead?

Did you not see the additional options available to you on the header when you press V to stitch, including the option to switch islands

Oh, I guess I never noticed it was swapping out the header like that. Thanks.