[2.0.0 nightly r4847] dropping any clef on staff yields a treble clef
Win 7 x64 OS, latest nightly build (r4847).
When dropping another clef on a measure in a score (e.g. to avoid lots of auxiliary ledger lines), you invariably get a treble clef. For example, dropping a tenor clef on a measure of a cello score in bass clef yields a treble clef instead of the tenor clef.