who/what deletes the print job?

Question

Having a strange problem where a print occasionally is not being printed

The scenario is that we print barcode labels with a barcode printer (Zebra LP2844). Printer is plugged into the TerminalPC and then shared.

Printer->TerminalPC -> Terminal Server. Session on TerminalServer is using Printer as \TerminalPC\Printer

When logging print Events we see the following:

Print OK:
1) Print OK (Event 10, User myUser)
2) Print deleted (Event 13, User NT-AUTHORITY\SYSTEM)

Print not OK => only Event 2) appears in the event log

Anybody having a clue about what is happening here?

More information: This problems occurs about 2 out of 10 times. Only difference is an increasing ID being printed as part af the barcode. The barcode is the only object being printed. It saves to file (*.emf) every time - and looks fine on file. The application is developed using Delphi 2010 and works fine in all other ways.