I was chasing this problem for a teacher who had covered for one of his colleagues in the Fall term. It was then the Winter term, and he was still seeing the other teacher's section whenever he created an assignment for his own sections (he taught 2 sections of the same class that he had covered for the other teacher).

As a result, every time he created an assignment, he had to manually unselect the other teacher's section so as not to accidentally assign his homework to the other teacher's section (a process that he was careful about, but not 100% successful with) and he wasn't able to use the Select All or Clear All buttons when setting due dates.

In discussion with Blackbaud support (ticket #019633475), it became clear that:

1. There was no mechanism in the user interface to remove that third, non-current section from the teacher's list of sections when creating assignments.

2. That any teacher who had ever had any relationship with the class -- even if that relationship was not in the current term -- was able, by design, to create assignments in the class.

I assert that #1 is annoying, but that #2 is defective by design. Only teachers who are teaching a class in the current term should be able to create assignments. And that in a multi-term class, a relationship in a previous term is demonstrably NOT an on-going relationship. It was ended. By the end of term.

We are never ever getting back together again.