HI Craig,
I can not find an option for Explicit Clefs in the import xml preferences, but that is certanly the problem. After importing the xml the (Explicit) Clef can be selected (write mode) and “deleted”, apparently nothing happens (the clef remains the same, at least in the file i tested), but 1. the clef can not be selected anymore and 2. the clef overrides function works as expected.
Thanks a lot.