It's indeed a matter of how you booked:

If the booking was made directly with 4U it resides in their crippled low-cost system. No e-ticket, no rebooking from there to LH or any other airline. It's technically not possible (and even if it was - the 4U call center folks probably wouln't know how to do it ).

If you book through a travel agent or on the LH website the price will be a little higher, but the booking will be created in a decent GDS and you get a 220 ticket number. When irregularities occur these bookings and the associated tickets can be endorsed to other airlines.