Would you like to try out this SSMPropEditor beta in your environment within the few next days?
What has been improved in this version is the locking of the Sheet Set. If the Sheet Set is locked you can open it Read Only in SSMPropEditor and if it is not locked SSMPropEditor will add a lock on it so you cannot modify it within AutoCAD even though you can open it. The aim is that it should play more nice with AutoCAD this way.
Please contact me either as existing customer or if you just want to give it a try.