No, not strange at all. If rebooking before outbound flights are flown, the entire ticket will be repriced based on (higher) current fares. If rebooking after outbound segments are flown, HISTORICAL prices will be used, i.e. if the same booking class is available there is no add. fare to collect. If booking class is not available, the fare difference needs to be paid (but again a fare difference based on historical fares/the fare that was used when ticket was issued). So if very lucky, W class is available for the new travel date, and rebooking can easily be done. LH might have started to change fees again by now and Exp might charge a fee for their services that is why the OP should contact LH first to see if LH is prepared to do the rebooking, but the costs of rebooking the return flight should not be significant (depending on the fare rules ofc).

If W class is not available (which is very likely given the current demand for travel) a fare difference will be calculated to be paid in add. to the mentioned fees. This is can be a high amount if the flight is close to being sold out and only the higher booking classes are available, but most likely it will still be lower than $ 1100. If the flight is far from being sold out the fare difference should be reasonable.

Let me put it this way: If there is no change to/rebooking of the outbound flights, then it would be crazy/it doesn't make sense to rebook the ticket before travel. If only the return flights need to be rebooked you wait until after outbound flights are flown. There is also a better chance that W class/other lower booking class will be become available again close to the date of your return flight than weeks/months before.