duplcate contacts in eM client

Contacts get duplicated when I send an email. the contact selected in the “To” box gets added to my contact list, duplicating the entry. Is there a setting to prevent this? I’m using version 5.0.

does it really add the contact to your contact list or it only shows duplicated in the suggestions list(drop down list shown when you click into the To field)?

I just checked three mails sent today and none of the addresses duplicated. Could a second computer on the same network be duplicating addresses? I have one also using eM client and the same contact list.

No, the second computer should not have any effect on this behaviour.