We are seeing a similar issue; I am emailing and referencing this ticket in case the OP did not.
Perhaps it is relevant that in my case, the merge was done in a HgFlow kind of fashion where the merge into default came from the closed tip of the feature branch, whereas BitBucket's PR merges are merged before the branch is closed? Or perhaps that's a red herring: just a thought.
@Petter Haggholm it looks like it is the case that the PR and the actual merge came from different branches, leaving the PR orphaned. The best way to capture and close out this PR will be to make a new branch and merge the PR into that. That branch can then be managed as needed.
@Silvia Ono please create a support issue so we can help make sure you get the most out of Bitbucket.
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