I have a case where the project name field of the copy artifact build step remains empty after saving the job configuraiton.

This happens when the source job is in the same folder (cloudbees folder plug-in) as the current job (the one that copy artifacts) and the current job is a multi-configuration job. See the following for a configuration example:

• Test (Cloudbees folder "pseudo-job")
• Test/Job1 (freestyle job that saves some artifacts inside the 'Test' folder)
• Test/Job2 (multi-configuration job that try to copy Job1's artifacts inside the 'Test' folder)

Note that I don't see the issue if 'Job2' is a freestyle job of the 'Test' folder. I don't see the issue neither if 'Job2' is a multi-configuration job not placed in any folder ('Job1' remains in the 'Test' folder).