It seems that when querying objects, users or user groups, the Operation type doesn't really make a difference. I forgot to explicitly tell the (C++) enginio client to use UserOperation when querying for certain users, and it works fine.
Is the operation type maybe calculated implicitly, and the specified Operation ignored? I am asking this because I am writing a wrapper class, and I wanted to calculate the operation based on the given object type. But if this is done already internally, I can save myself the work.
Sadly you can not always calculate the operation, that why it exists.. It may happen that a query works as expected with a wrong Operation, but this is an undefined behavior.
OK, thanks, I will deal with it appropriately then.