Naval Administration building / Fleet relation quirks

I'm just kind of confused about how the NA assignments are supposed to work.

You can't build NA in a region if you don't have a fleet there. Which kind of makes sense (especially if they're supposed to be related). But then I create a new fleet in Northern China, build a couple NA levels in Shandong and transfer a couple frigates there. My new fleet shows that it's tied to the NA building in Shandong. So far so good.

But then the actual ships are still taking their crews from Fujian where they previously were.

Shouldn't either the crews shuffle around to Shandong (as long as there is manpower available), or at least the Northern fleet list a connection to Fujian naval administration it's actually still drawing crews from?