When a branch got deleted before the Jenkins Jobs finished build, seem like Jenkins chose to notify Bitbucket that the commit it execute was finished. This give some issue when the branch been delete, and later push back to server with addition commit, or some time these commit end up in master branch. Then we see that commit still indicate "In Progress" by Bitbucket forever, many, many year after.

I would suggesting always send notify to Bitbucket regardless. Since a Bitbucket tracking the build by commit hash, not branch (I believe).