Adding Messenger Friend creates Two entries in outlook.com People

Adding a messenger friend appears to create two entries in the outlook.com people contacts - one for messenger and one, with an email address only, as an outlook.com contact.

If you have an existing outlook.com contact and merge these, outlook.com seems to lose the ability to send messages through messenger to this contact.

Does anyone know what the second (outlook.com) contact is for - don't especially like having contacts with two outlook contacts plus all the others, but if one is for the Microsoft Account and the other for Messenger, then this would make some sense - but it would be better if this showed as such on the contacts so that you don't delete important contact details when tidying up contacts!