If I have 48 radiation samples in my bank and 6 in my inventory. I grab the 6 from inventory and drop it on the 48. What I would expect to happen is that 2 would stack with the 48 to the stack limit of 50 and the remaining 4 would drop into an empty bank slot.
What happens is that the 48 and 6 just swap places.
I do not see a way to split stacks. I might have missed this along the way. I would expect to right click and be able to chose how many I want to split into a new stack.
You can split stacks by using CTLR while dragging.
I'll try that when I get on next. Thanks for the info!
EDIT: It's CTRL+left-click-drag the item stack to another inventory slot. A window will open asking you how many of the item you want to move (I use it for splitting up power cell, hypospray, and shield charge stacks to share with my BOs).