I have confirmed that adding "greeter-hide-users=true" in the SeatDefaults stanza of lightdm.conf fixes the problem.
We would still like to have the behavior I saw before, where if a user was known to the accounts manager, they would be listed, but there was always an "other" box also. However, this workaround is acceptable (and certainly no worse than gdm--lightdm is still very very nice), so fixing the bug itself is now lower priority for us.
I have confirmed that adding "greeter- hide-users= true" in the SeatDefaults stanza of lightdm.conf fixes the problem.
We would still like to have the behavior I saw before, where if a user was known to the accounts manager, they would be listed, but there was always an "other" box also. However, this workaround is acceptable (and certainly no worse than gdm--lightdm is still very very nice), so fixing the bug itself is now lower priority for us.