Note appearing a step too high?

I'm working on a viola transcription of Schumann's Phantasiestücke, Op. 73, and for some reason there is a single note that is appearing a step higher than it should. This is in measure 17--the octave leap up from C in treble clef. It's playing back correctly at pitch, but just appears as a D for some reason. If I move it down a step, the second ledger line disappears entirely, causing it to look like a slightly levitating B (which is also the pitch that sounds).

This is a very minor issue, but would be nice to clear up since the whole purpose was to make myself a cleaner performance part.

When the same figure comes back in measure 53 there's no problem--the ledger line doesn't disappear and C sounds in the correct place.