Either there is a small bug with the default “short names” for instruments, or my defaults have somehow gotten messed up. The issue is this: some of the short names include a period after the abbreviated name of the instrument, and some do not.
Instruments that include a period after the abbreviated name:
• All of the orchestral wind instruments
• Trumpets, trombones, and tuba
Instruments that are missing the period:
There are surely many more in both categories — this is just a quick check. I think all the abbreviated short names should include the period.