If an oai context contains for example 2 virtual sets.
S1. Items with dc.identifier.doi
S2. Items without dc.identifier.doi
and wie have 2 Items:
A with doi
B without doi
then as expected:
S1 only contains item A
S2 only contains item B
But if you look at Item A with GetRecord than the record shows that the item is part of S1 and S2 which is false.
This is due to a bug in the xoai library:
It add's a set to an item independent of the filter.