Hi Tobias,
it seems to be a little bit more tricky when reserving batches in SO. You can pick everything ( ReleasedQuantity / the exact batch quantity choosen in SO) but you can not easily pick lower quantities ( at least I was not able to find a way ).
Apparently the batches are not saved / managed in the picklist ( PKL2 ) but in the document ( no BatchNumbers lines ).
For me it looks like a bug or at least missing feature in DI - maybe I am missing something..
regards,
Maik