GroupWise Mobility Service & iOS 13.1.3 - Duplicate "sent" items


if we send Mails with iOS 13.1.3 devices, the sent mail shows up normaly in "Sent Items" but after 1 or 2 minutes, we see in sent items the mail two times. Looking in GroupWise sent items, shows only one sent item.

Tested on different iPhones with iOS 13.1.3, same problem.

Configured another Exchange Account (different Domain Exchange Server - no GroupWise Mobility Service) on my iPhone and tested the same and no problems.

Seems to be a problem with GroupWise Mobility Service. Any ideas how to solve this ?

Thanks and regards.