I'm trying to envision what U1 could have done that would be different than what you are used to in FED 3 umpire mechanics.
AFAIK, the coverage for the play you describe is no different, U1 has all plays at 1st and 2nd and the B/R to third, PU would have the lead runner at third and home.
Then it occurred to me...did U1 stay outside the diamond instead of coming inside and using a buttonhook? That would be something that is allowed in the college mechanics, but not in the FED manual.