Has anyone experienced students enrolling in 2 classes that overlap in time, and not get a Time Conf

We are experiencing random students being able to register for classes whose times overlap, and not receiving a Time Conflict error. When we try to replicate the problem, we get the Time Conflict error. I tested this as a student through the portal, as well as quick-enrolling them as myself for the student. It seems to be sporadic, with no pattern that can be identified. Anyone have any ideas?

Thanks very much,

Adlai