I have created a Multibranch Pipeline Job and have configured the Branch source section setting the values for Credentials, Owner and Repository. The strategy for discovering branches is set to 'Exclude branches that are also filed as PRs'.

After saving the configuration, a scan repository is executed and a build for each branch that meet the criteria is scheduled. In my case, that makes 3 build scheduled and master ignored because it doesn't meet the criteria. This behaviour is right up to here, but the message in scan repository screen shows '4 branches were processed' although only 3 builds were scheduled. Using github-branch-source-2.0.8 the message shown was '3 branches were processed'.

See screenshots attached.