ListModelSet retainAll doesn't work properly

The method retainAll from ListModelSet retains elements not present in the collection passed as parameter.

Example (attached java file):
ListModelSet: A, B, C, D, E, F
retainAll(C)
Result: C, D, E, F

I would expect to only find the C element in the ListModelSet.

I executed the same test with ListModelList and got the expected result (only C is present).