Switching an existing PR from branch A to be against branch B doesn't force the status checks to re-run.

I've set a priority if Major as this 'loophole' allows changes to go into a branch without the proper testing.

The flow to expose the 'loophole' is:

1. Open a PR against  branch A 
2. Once all builds complete and the 'check's have passed
3. Then change the PR to be against branch B
4. The previous 'checks passed' state remains despite the change in branches.
5. User is allowed to merge that change into branch B without running the proper test (ie. build and smoke tests)