Can't move stacks to the right side of the workspace — not enough space?

[Guntis]

Hi,

I have 2 panes open in my workspace which is across the whole screen (15.4" retina MBP). I select something in the Bible text, press Stacks icon, text is copied to the Stacks and the Stacks is open in the bottom part of the workspace. I want to position Stacks in the right side of my screen, but I cannot. Accordance complains that "There is not enough space to move this item into that Worskpace of Zone". I disagree. There's a lot of free space!