Here you are. The test case is attached. What I have found creating the test case is the following:

• the bug is not triggered for a plain CompositeUserType attribute which is composed of simple types such as IntegerType or such
• the bug is not even triggered for a CompositeUserType attribute which is composed of plain CustomType(s)
• the bug is triggered only for a CompositeUserType attribute which is composed of CompositeCustomType attributes - two levels of Composite types are required.