How are IDs handled when converting an existing entity into a specialization of a new generalized entity?

Currently, we have existing table A with data that we want to convert into a specialized entity. 

Here is what we are currently seeing:

• table A has IDs 1,2,3,4 and these get converted to a generalized table B
• we then create an objects in table C(inherits from B) and they get IDs 8,9,10
• If we go to create another object in table A it is given ID 5 - I would have expected it to continue with ID 11

This makes it look like there is a possibility of the ID collision in the generalized table. Are we misunderstanding this, or does Mendix handle this scenario and make sure 2 objects never have the same ID?