When shift left-clicking a stack of items in the bag, bank, or reagent bank, the 'splitter' UI appears behind the bag bank window
(version 0.0.24)

Does it appear behind the player bag too, or just the bank?

Okay, this makes sense. I layer the bank "above" the player frame, but i might instead layer the player frame "under" the bank frame. Let me do some testing.

Oops - Infront of bag, behind the bank windows.

Fixed in the next release. Thanks!