I just saw that when I choose a test case to associate to a work item, it automatically removes any previous associations the test case might have had.
The problem I have with this is that there is no warning of any sort.
So, if I don't know that I can only have one-on-one associations between a work product and a test case, I would keep adding the same test case to multiple work products and assume that they are all being tied together. Until it's too late!
First off, it would be great if Rally could automatically create a duplicate of the test case that is already associated with another work product and assign it to the second work product. Even though this is not how it is currently, the least I would expect is to warn me that my previous associations are being removed.