If you use the +/- keys to navigate through SFX positions, and then Cmd+C (Mac) to copy, it actually copies the SFX that was last selected by mouse (rather than the currently selected SFX).

To reproduce:

1. Make two different SFX patterns in 00 and 01.
2. Select SFX 00 with the mouse.
3. Hit '+' key to select SFX 01.
4. Press Cmd+C.
5. Select SFX 02 (using mouse or keys, doesn't matter).
6. Press Cmd+V.
7. Note that the SFX pasted will be 00, not 01.

I've only tested this on Mac but I guess it's likely the same on Windows (with Ctrl+C).