I finally figured out the problem.
To recap: the problem is that when holding paper A, the game wasn’t allowing the player to take paper B (which isn’t takable, but I want them to try), and was always choosing the carried paper as the subject of TAKE.
The problem is that paper B is undescribed. Making it scenery also causes this problem. I suppose that since scenery is not takable, the game is disambiguating to the carried paper. Weirdly, making it undescribed also causes this behavior.
Is there any way around this?