Describe the Bug:
Unable to reorder a rotation in which a user participates more than once

Steps to Reproduce:

1. Create a rotation with the same user multiple times
2. Reorder said user
3. See error

Expected Behavior:
Reorder a rotation reliably, even if a user appears on it multiple times

Observed Behavior:
Unpredictable behavior, console errors

Application Version:
1bb362a8ce0c087efbe61b129ae15713f8508f65