Program Change (Banked)

I bought a new keyboard (Viscount Legend One 73) that I can use as a masterkeyboard.
It has an internal sound engine too. Now I wanted to access the internal sounds with “Program Change (Banked) to “External Synth” in"Song - On Load” but it seems that the Bank MSB/LSB are ignored. I can only reach the first 128 presets.
This occurs in the latest versions of Cantabile v3 and v4.
Any help appreciated.