For pull requests I use merge strategy Squash Source Branch Commits to keep the git history clean after merge. However when using this strategy the final commit into the target branch is generated from the pull request title and description. That is why I started to write the fixes issue text into the pull request description and not in any of the commit descriptions contained in the pull request.

When opening such a pull request the issue state transition when pull request is opened with issues matching fixed in current pull request does not work. I guess OneDev only looks at the commits of the pull request but not into the title / description of the pull request.