Merged thread always marked as read

[despecial]

Problem: a merged discussion is always marked as read even though it moves up on the front page for new replies.

The discussion was created from splitting posts to a temporary discussion (and then renamed)
In my case, I afterwards used the "change post author and date" extension to move the initial temporary start post back to the top. The split replies were older than it, of course.

[poVoq]

Same problem here on Flarum 1.7.x but I only merged a newer discussion into an older one, no other changes.