Records of verification, which I will assume you are using these tests as a part of, are critical in any audit / inspection of design controls. In every design control audit and inspection I have been through, good verification records have always helped lead to positive outcomes.
If the testing you are running will become part of your formal record of verification, then you should have records showing why and how those test cases changed over time. Using a bug report against the test case is one way of doing this. The record should include why a change was needed to the test (in this case the bug), what change was made, who made the change, who reviewed and approved the change (the review/approval should be someone other than the person making the change). Test cases are no different than other documents in that the test cases must be reviewed and approved before they can be used and any changes to those documents must be subsequently reviewed and approved.
You also need a record that the updated test passes. You could have someone approve the necessary modifications as you are running the original test and then the subsequent review is to verify you documented what was done in the test case, or you could update and run the updated test case prior to completion of the verification. I am sure you can come up with other options as well to satisfy the regulations.