Normally for me its the other way around!

Entire flight is ticketed as UA. But first leg is on LH, second leg is on UA.

When I go to United to check in I get rerouted to the LH website and I check into my first flight.

I get my boarding pass for the first flight from LH but it won't give me a boarding pass for the UA leg.

When I go to the UA.com website it doesn't show me as checked in so I can't print the boarding pass.

I know I can get the boarding pass at the airport, but there have been times when UA has not been able to get me *A carrier boarding pass.