No references shown after copy a drawing model

Hi to all,

I have the following question. I have an existing DGN file with 3 types of models in it, design models, drawing models and sheet models.

If I go to the model dialog and I do "copy model" from existing design model, then this model is copied and all the references are perfectly shown into the references dialog.

If I do the same with an existing sheetmodel, then also the references are present in the references dialog.

But if I do "copy model" from an existing drawing model, then the references dialog shows no references! After I close the DGN file and reopen it, then alle the references are shown again in the references dialog.

Is this a known issue? Is this a bug or does it work differently with drawing models?

Can somebody explain the differences to me? I would be very thankful.