I'm sorry for my confusing previous post: you surely aren't using the SAP* user itself for your tests.
Then again, when a structural profile is assigned indirectly through this construction, it may be that determining the correct starting point for the FM is indeed the culprit.
It could be that the T77UA table is taken into account while determining the required US<-->P relationship.
If this is the case, it makes sense that no objects are found since SAP* does not have a related P-object and therefore cannot find a starting point for the FM.
I think you could easily check that and assign SAP* to a PERNR to see if you do see objects then 