Hello,
This issue seems to be resolved as I haven't come across any of such cases with Symantec Endpoint Protection 12.1 detecting DWH###.TMP files
Was this SEP 12.1 clients upgraded from SEP 11??
http://www.symantec.com/docs/HOWTO55365
The Above Article, speaks on how to clear disk space before upgrading the SEP 11 to SEP 12.1.
The Actual cause was with SEP 11 where the files were created by the Symantec Endpoint Protection or Symantec AntiVirus Quarantine scan. This scan is normally initiated by a virus definition update.
The quarantine scan on virus definition update can be disabled: edit Antivirus and Antispyware policy > Windows Settings > Quarantine > General, under "When New Virus Definitions Arrive" choose "Do nothing".