wrong MIDI playback after transposition change

[jacekiwaszko1]

When you change the transposition during one piece, it displays nicely, but MIDI playback is not good:

**kern	**kern
*I"without transposition	*I"with transposition
=	=
!	!LO:TX:t=in C
1cc	1cc
=||	=||
*	*ITrd1c2
!	!LO:TX:t=in B
1cc	1cc
=||	=||
*	*ITrd2c3
!	!LO:TX:t=in A
1cc	1cc
=||	=||
*	*ITrd-2c-3
!	!LO:TX:t=in Eb
1cc	1cc
==	==
*-	*-

I would expect those two parts to sound unisono, but they're not - part with transposition plays, as if it was encoded as

**kern
=
1cc
=||
1dd
=||
1ee-
=||
1a
==
*-

Is there a way of fixing MIDI playback?

(originally posted in closed #280)

[craigsapp]

Reposted as issue #549 to bring it to the top of the list of issues.