Remove unwanted Clef and Key Signatures in MS4

Open an MS3 score in MS4 - in this case horn octet. Each time there is a clef change in ONE of the parts, all 8 get a clef sign and key signature (7 redundant clef signs, 8 redundant key signatures).

Here's the "bug":

Scenario: Painstakingly highlight and delete each unnecessary clef sign (one by one); highlight the column of unnecessary key signatures, drag and drop "open/atonal" signature; highlight the resulting (now incorrect) column of key signatures and delete. Happy with the result?

BUG: "Save" the corrected version and all the edits are lost. All the redundant clef signs and key signatures are re-instated by MS4.