See jenkinsci/throttle-concurrent-builds-plugin#57 and jenkinsci/throttle-concurrent-builds-plugin#74.
Note that if you are encountering any issues related to this change, the old behavior can be re-enabled by setting the Java property hudson.plugins.throttleconcurrents.ThrottleQueueTaskDispatcher.USE_FLOW_EXECUTION_LIST to false.
Fixed in jenkinsci/throttle-concurrent-builds-plugin#57 and jenkinsci/throttle-concurrent-builds-plugin#74.
Released in Throttle Concurrent Builds 2.0.2.