Can not create invoice when item in SO is on back order?

Can not create invoice when item in SO is on back order?

Hello, 

Ran into a hiccup today when I tried to use the Backorder feature for the first time. 

Why is the whole order placed on hold when 1 line item is on back order? A lot of the time, customers want to pay for the complete order even if we do not have item in stock. 

Is there something i am missing? 

Thanks