From the Roland Arranger site:


As explained previously the OS3.01 was initially sent out solely to Roland Germany as a bugfix aimed directly towards an specific bug claimed by Roland Germany. Therefore the release was initially not an official release. However, the version 3.01 has now become an official version, because the Roland Service Dept. officialized it.

I have this confirmed information about the content of the version 3.01: the update only fixes a specific bug in the harmonizer section; there are no new data, no new feature, no improvements in sounds or other.