[JIRAALIGN-1284] A user is assigned several times in a sprint

Issue Summary

A user can be assigned multiple times into a sprint.

Steps to Reproduce

Not easy to reproduce but suddenly occurs on some customer and test instances. Basically, you will just notice that a user is assigned several times to a sprint.

Expected Results

A user can only be assigned to a sprint once.

Actual Results

A user is listed several times in a sprint assignment.

Workaround

"CLICK HERE TO COPY ALL MEMBERS FROM THIS TEAM INTO THIS SPRINT" will clear the duplicates but the user has to reassign everything again.