The only part of the MIDI officially supported in the RPC-1 are the "System Common Messages", the "System Real Time Messages" and the "System Exclusive Messages".
This means all the messages that DONīT contain channel information in the first byte.
Although the R-Bus protocol in theory can support all the MIDI protocol v.1.0, only the system messages were implemented in the RPC-1.
Look that the drivers are completly compatible in the audio side, but the MIDI shows different degrees of compatiblity depending of the computer, the Roland V-Studio or the Roland mixer that you are using.
At the present I only can test it with the VS-2480 and for me the MIDI works well in a 90 %, but I don't use the whole implementation in my daily work.