I have a job that can perform concurrent builds.

As post-build steps I have both Perforce: Publish assets and Perforce: Cleanup.

The Publish assets action on the concurrent build results in:
P4: Unable to setup workspace: com.perforce.p4java.exception.RequestException: Error in client specification.
Embedded special characters (*, %%, #, @) not allowed in 'C:\Program Files (x86)\Jenkins\workspace\test-project-assets@2'.

ERROR: Step ‘Perforce: Publish assets’ failed: P4: Unable to setup workspace: com.perforce.p4java.exception.RequestException: Error in client specification.
Embedded special characters (*, %%, #, @) not allowed in 'C:\Program Files (x86)\Jenkins\workspace\test-project-assets@2'.
 

If I remove the Publish assets step and only perform the Cleanup step I get:
P4: Template workspace not found: jenkins-master-test-project-assets_TEST
P4: Unable to setup workspace: hudson.AbortException: P4: Undefined workspace: jenkins-master-test-project-assets_TEST.clone2
ERROR: Step ‘Perforce: Cleanup’ failed: P4: Unable to setup workspace: hudson.AbortException: P4: Undefined workspace: jenkins-master-test-project-assets_TEST.clone2
 

The exceptions do NOT occur on the first concurrent build.