We have applied a software engineering process to code reviews of pull requests that involves numbering issues in comments on the code. When the issue is resolved on the branch of the PR, the developer will frequently refer to the issue number from the comment on the PR in their commit. However, making such a comment in a commit resolves an unrelated issue on the bitbucket issues list.
I believe it used to be that if you did not use a hashtag in the comment on the commit, this behavior of resolving a bitbucket issue in the issue tracker would not occur, as I have been unable to find past such commit comments that had this effect. In order to have confidence in knowing what will happen as the result of entering free text in a comment, I believe it would be better to require hashtags on issue numbers in order to auto-resolve bitbucket issues. Otherwise, there is a conceptual collision of issues in the issue tracker versus issues in a pull request comment.