Merge-commit <hash> can't be remerged if none of its parents was seen in the rebase

[Byron]

From Discord.

Not sure if this already came up: When I try to update my workspace (via the Update button), I get an error with the following message:
Merge-commit 8c1954309f6e37ec856b1017c5c2ae6f548eebc0 can't be remerged if none of its parents was seen in the rebase (to be replaced with this new commit)

However, if I unapply my currently applied branch, then update my workspace, and then reapply the branch, everything works.

Theory:

This looks like V2 'update integration branch' code runs V3 rebase code. There one could be on the lookout for the infamous base_substitute.
Maybe that's not easy to do as the V3 rebase is launched from cherry-rebase-group.
In any case, next time we have a repo that runs into that we should keep it so it can be patched while we wait for the pure V3 version of the same functionality.

[mtsgrd]

@H1ghBre4k3r I've run into something similar, when I had a branch checked out with a base newer than the workspace. Is there any chance that was the case for you?