It seems like there is a kind of 'race condition' when accepting a revision that was already accepted by one of the projects a user belongs to.
- Create a project X, add users A and B as members.
- Open revision page as user A.
- Open revision page as user B (in another browser).
- Accept revision as user A on behalf of Project X.
- Accept revision as user B on behalf of Project X.
- Validation error
phabricator 53bc57ecef8739c29105eb52b1f118c0402e2c6c (Sat, Apr 29) (branched from d2baa88171fcc3f327b157277afb905430b5a918 on origin) arcanist ada63de9722e4b60ec9f0900a757b5b3873fc2f7 (Sat, Apr 29) (branched from 27b51e619237116d99e03fc1b3e8cd6399087214 on origin) phutil d02cc05931b02c684d4c729510090591ca45f951 (Sat, Apr 29) (branched from a900d7b63e954e221efe140f0f33d3d701524aae on origin)