True. This is a limitation as a derived element has just 1 ID field. It picks the first one and ignores the rest. (as documents in a DocDB for instance don't have compound PKs either).
That said, for this particular method, it could perhaps be fixed if the template would check whether all fields in the PK of the entity type are in the derived element and if so, add them to the comparison.
(edit) the change will not be made to v5.3 but to v5.4 at the soonest, as it's a breaking change.