Minor Section 11.3.1 Delta Links describes handling of delta queries in combination with $expand, the relevant text is attached below. The highlighted sentence seems contradictory and should be clarified. It demands that the delta response must include changes to the expanded entities also for navigation properties expanded with $ref, whereas the following paragraph states that a delta query with a $ref expansion will ignore changes to changes to related entities.
"If the defining query includes expanded relationships, the delta link MUST return changes, additions, or deletions to the expanded entities, as well as added or deleted links to expanded entities or nested collections representing current membership. This is independent of whether related entity themselves or only references to related entities were requested.
Navigation properties specified in the $select list of a defining query are not used to define the scope or contents of the items being tracked. Clients can specify /$ref in $expand in order to specify interest in the set of related entities without interest in changes to the content of those related entities.“