Scratch

I'm currently working on a new program for making music in scratch, and it has lots of different sprites which have music blocks. Most of these sprites also have different instruments. It was all working fine until I made a new sprite (with NO music blocks) and suddenly one of the sprites with music blocks started changing its instrument to that of another sprite, and no matter what I tried both of these sprites insisted on using the same instrument. So in the end, after deleting most of the sprites hoping that would work, I tried moving the music blocks from one of the sprites with the problem to another sprite which until then didn't have music blocks, and this seemed to work. But THEN, the next time I opened the project, it happened again! This time with two different sprites and when I tried the same thing as above, it did it again with two new ones!

If anyone has any ideas on how to fix this (or how to manually assign MIDI channels to sprites), then please help!