I’m not sure that I can explain this without adding to the confusion, but I’ll try.

When you use the program menus to select Composer, and then Custom Copy, you can copy in either direction. That is, you can copy from the Composer to Custom Memory or from Custom Memory to the Composer. If you assume that you are copying from the Composer to Custom memory, when you do that, the contents of Panel Memories A, B, and C are also saved in the Custom memory of the keyboard, along with Composer banks A, B, and C. The same occurs when you copy in the other direction.

If you simply select one of the Custom memory rhythms for playing, nothing changes in the Panel Memory banks and you can play whatever rhythm you select with whatever was already in the Panel Memory banks. BUT, if you do a custom copy from Custom Memory to the Composer, using the Composer menu, you also copy whatever Panel Memories that were there when the Custom Memory was initially saved, to Panel Memory banks A, B, and C. So, in that case the Panel Memories will change.