Hi everyone,
Good news: this bug has now been fixed.
Previously, when using buttons to navigate between pages in a published Coda doc, the linked pages would always open in a new browser tab. This only happened in published docs and did not occur when viewing the same doc in unpublished mode.
The issue was related to how OpenHyperlink() handled published doc URLs. Published URLs were not being recognized as part of the same doc, so they were treated like external links.
With the fix in place, buttons that navigate between pages in a published doc should now behave as expected.
Thanks to everyone who reported this and shared details to help us track it down.