Media bay causes external instrument to drop out

I have one external instrument set up in Cubase. Cubase ceases to send MIDI data to my external instrument when I perform the following steps:

  1. Open media bay
  2. Select an instrument track preset. This loads an EastWest Play instrument.

If I playback my track while media bay is open after performing these steps, the external instrument receives no MIDI. If I perform the above steps while my track is playing, my external instrument ceases to receive MIDI in the middle of playback.

Is there a way to stop this from happening? My objective is to use media bay to audition various instruments while my track is playing. I can’t have my external instrument dropping out every time I audition an instrument.