After you build a test run, if you need to remove a test case from the run, it’s not all that intuitive. Once you understand that you’re basically pulling test cases and their history into a different view (rather than the test run creating a separate instance of the test cases), it kind of makes sense. However, the risk in this functionality is where you’ve manually selected many test cases for your run. If you apply a filter when selecting (and de-selecting) test cases, it seems you lose all your previous selections. You would then have to rebuild your entire test run when maybe all you really wanted to do was remove one test case.
We managed to get around this by created a custom value in Status called “Skipped” so that testers don’t have to inherit this risk to the team. I suggest reconsidering this functionality to let teams remove test cases in a much simpler way. (As always, if I’m missing something here, please let me know.)