When a user opens a pull request, some references are created inside the Git repository hosted in the Stash server. These references live in files stored in <STASH_HOME>\data\repositories\<REPO_ID>\refs\pull-requests\<PULL_REQUEST_ID>
This is great and allows one to, for example, configure the build server to build pull requests and the result of the merge.
However, these references are never deleted from the Git repository, so there's no way for a build server to know when to stop monitoring these references. Because of that, if you merged 1000 pull requests in the past, the build server will show you 1000 build results, one for each pull request, even though you already merged (or declined) these 1000 pull requests and are not interested in these build results anymore.
I would expect the reference to be removed after the pull-request has been merged or declined. If a user reopens it, then the reference should be recreated.