Migrated questions get rejected if they are closed on the target website, with the exception of duplications.
Earlier today I saw that a question was posted here and on MathOverflow simultaneously (with links), and that the MO question had 4 migration votes. I voted to close it there, and when it arrived here I used my dupe-hammer to close the migrated question as a duplicate.
I then proceeded to flag it for merging with the original post on this site, which indeed happened shortly after. But then I noticed that the migration was rejected, which makes no sense.
Is this somehow by design, or just an unnoticed bug?