Hi Chris,
Thanks for that breakdown — I had assumed you meant that!
For the end user, it should be the case that they only gain access to the new changes once they have been released from the preview view of the app. I’ve tested this on our side, and it’s working as expected.
To confirm the steps:
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A new branch is created from main, edits are made, and a PR is pushed into the source branch (production in this case).
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The app is viewed in preview mode — changes are compared, and a release is made. See screenshots attached.
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The end user can then see the updated version.
That said, this process only applies to the end user. Any further development work or new branches a created are created from the source branch, not from a version. And so all the merged PRs are visible to editors.
If this is not the case could you share more specifics on your steps of how the PR is being merged into the source branch and how this is being shown in your ‘live’ releases.
Within the release modal, accessed from the app preview, you should be able to view the release history which will include the merges from source control and when they were moved to live. Please see the screenshot below where you can see the most recent merge and how it has now been included in the live release. I would hope this should give a good indication as to what might be happening here.
For a more detailed explanation, here’s a great breakdown of how releases and can source control work together: 
Using Releases, App Versioning & Source Control Together.
Thank you!
Ollie