GroupWise 2014 R2 Support Pack 2
According the the 14.2.2 documentation:
2.5.2 Changing Your Display Name
You can change the name that is displayed in items that you send from GroupWise. You can only change your display name if the Accounts menu is displayed. The Accounts menu is displayed if you are in Caching mode or if your administrator allows POP and IMAP or NNTP on your GroupWise system.
1 Click Account > Account Options.
2 Click the Mail tab, then click General Options.
3 Type your display name in the Display Name field.
4 Click OK, then click Close.
If you perform the steps above with 14.2.2 client or above, the Display Name will never change in the email.
This has been reported to engineering for a change in the documentation. The behavior is actually working as designed in the client.