In the job configuration when "Promote builds when..." is enabled, in the criteria of the "Promotion Process", "If the build is a release build" is duplicated.

If both are checked and the job is saved, upon next open of the config, "If the build is a release build" criteria is unchecked.

If one is checked and the job is saved, upon next open of the config, "If the build is a release build" criteria is enabled.

The effect of this is that the option is toggled each time the config is edited and saved and means it cannot be relied upon.