Oracle 12c: sql query return less result when it's used in a subquery

Question

I recently encountered a weird situation where i get different result from the same query by only changing its scope.

What i mean by changing the scope , is putting the query inside a subquery:

I have this query:

select * from my_function

It returns the correct result, but when it's used as a subquery it gives less result :

select * from (select * from my_function)

Please note that there is no filters nor limits on rows.

my_function is a function that return a dataset like this :

return anydataset pipelined using myType;

I'm wondering if there is some (hidden) parameter in oracle 12c that might limits the result of a query when it's used in a view or a sub-query , especially if this query is using a function as source.

Thanks for your help :)