Today I closed question A as a duplicate of an older post B (ie. A was closed and B was open). Both already had answers. It was then decided the questions were similar enough to warrant a merger. It seemed to me that A was posed better than B, so I, from the mod menu in B, merged the two posts using a link to A as the "master post". All the answers and comments moved from B to A as expected, but the surprise is that A is still closed as a duplicate of B (ie. both questions are now closed/locked pointing at the other one).
This is not expected behavior and I'd even call it a bug. Please, when merging two posts where one is a dupe of the other (isn't that all question mergers?), be sure to reopen the master question. I'm going to manually reopen A now, but this should be automatic.