Can't modify user in Office 365 cause they weren't created first on on-prem srv

Hi spiceheads,

One more question heading into the weekend.

I have AD Connect Sync running, have a hybrid deployment setup with my Exchange 2013 on-prem server and O365, and have migrated all my users over to Office 365.

So here comes a brand new employee. I created the employee on my on-prem AD, waited for it to sync with Office 365, and then proceeded to apply the E3 license to the user. So now they have a mailbox.

Here's the catch - their login is correct, but their email is still the domain.onmicrosoft.com, and every time I try to change it, it complains that I have to change it on-prem and sync that change.

Well - if the user mailbox wasn't created with the on-prem Exchange server - how the hell do I adjust for that now. Does this mean that I will have to perform a migration each and everytime we add a new employee?

Got to be...