Why does this rotary switch register multiple positions simultaneously?
Figure 1. The "make before break" switch. Note the wiper (1) will bridge the adjacent contacts (2) when switching from one position to another.

These switches are used when you want to avoid disconnecting the signal completely when switching from one position to another. e.g., If your switch was used as a volume control with a chain of resistors wired between each contact tab then this will give a glitchless switching whereas a break-before-make switch will disconnect the audio momentarily resulting in a glitch.

The break-before-make variant will have a gap between contacts (2 above) to prevent short-circuiting.


  I programmed three distinctly different sounds to play back per each rotary position, and indeed, they never play simultaneously, only one at a time, upon 'arrival'.


Without a schematic diagram I can't comment on what you have done here.