VDB editor in Teiid Designer 8.6.0.Alpha1-v20140825-1403-B2763 allows me to add source model from reused VDB to new VDB.

The "New VDB" dialogoue accessed using New -> Teiid VDB doesn't allow me to do so (screenshot1)

But when I complete the creation of this VDB, edit this VDB and try to add new model using Edit VDB view, it allows me to add this source model without any warning. (screenshot2 and screenshot3)

NOTE: I can also get around this by selecting a vdb source model and right-click New > VDB ... it'll add the model to the VDB