Not sure what causes this, something to do with SetUserPlaced or the timing of that on login. I need to make a simpler case with a basic frame to test it's not a blizzard bug.

To replicate:

1. Unlock the bags (or bank, doesn't matter which).
2. Drag it out of the default position.
3. Drag it onto the snap point for the default position.
4. /reload
5. It's now back where it was before the snap.
6. Drag it a second time into the snap position.
7. /reload
8. Now it stays correctly.

Ths is fixed in 10.1.5-1 by no longer use the Blizzard auto-placement code.