Thanks for the feedback. Please feel free to add that as a feature request to our feedback site, so that it can be reviewed by the team and other customers.
I’d have to disagree that it’s a bug. Service previews are created when a PR is opened. If you’ve chosen to skip the preview for a PR for whatever reason, then it won’t be rechecked.
I guess it’s a difference in workflows. Personally, I only raised a PR when it is ready for review, so I want the preview created. If your PRs are created a lot earlier in a more developmental/unfinished stage, then I can understand you’d want to skip them until they’re ready.
The simplest workaround would be close and recreate the PR when the branch is ready for preview (not the best case, as you’d lose any conversation/comments, but a workaround nonetheless).
There are also other feature requests on the feedback site to be able to create previews manually from branches, which may also fit your use case. Then, you would have control over exactly when a preview is created.