Aha. I have a strange and unwise attraction to that very bad boy of Inform 7: “instead of”.
I had an “instead of” rule that I wisely changed to a “check” rule, but failed to take out the “if the player carries the paper” that made the instead rule work as I needed. It sucks to have such a reflexive tendency to use the very thing that will always, ALWAYS cause me grief. Got it fixed now.
Nothing to see here, folks. Move along from the train wreck.
ETA: well, crap. Not fixed. I think I probably need to revisit basic rules for changing text when taking or examining something. This is a whole lot of stupid.