Sunny,

All the Korg PA keyboards have very extensive MIDI control options - also the Pa50. You can set up to 8 MIDI IN filters that will block various incoming MIDI messages. In this case you should probably use the "All CC" and "SysExcl" filters. Look at page 129 in the Pa50 manual. Remember to save your global settings when you have made a setup that works.

Kind regards,
Tommy