Fixup error when saving entities using many-to-many relations

[aquisio]

After updating a stable Angular app from Breeze v1.7.2 to v2.1.4, I am seeing client-side errors when attempting to save entities that hold many-to-many relations.

I have documented my diagnostic procedure and observations in the following StackOverflow post: https://stackoverflow.com/questions/78315808. (Apologies if this is considered to be double posting).

I am not suggesting this is a Breeze bug, as I realize that I am probably doing something wrong in my procedure for creating new entities on the client, but I would appreciate it if someone can steer me in the right direction.

Many thanks, Tim