If an user drops a block on an internal block diagram a new part is generated. That`s the intended functionality. We noticed that a common fault is the unintended multiple creation of new parts by users.
An information for the user that a part with the same type is already in the model would be helpful to avoid multiple parts in the same IBD.
There is already a part typed with this Block in the model. Do you want to use the existing part or create a new part?