Channel conflict on MIDI export

Currently, when a score includes an instrument such as a strings or a trumpet which has different types of sounds, each types of sound uses a different channel. For example, trumpets use one channel for normal playing and one for mute playing. As a result, when the score is exported to a MIDI file, it does not play with the correct instruments. Even if the total number of instruments is less than 16, there can still be a channel conflict due to the use of multiple channels for some of the instruments. It seems to me that each instrument should only get one channel, and the patch on that channel should be changed when necessary for muting, etc.