Perhaps they are using it as some sort of crude, or ingenious, DAC.
Just a guess and probably not how it's designed:
If you wanted to generate a square-wave that swung between 1V and 3.5V you could feed these two DC voltages into pins 1 & 2, and get a square-wave out on pin 15 that toggles between 1V and 3.5V at the same frequency as the logic level signal on pin 10.
If the 1V and 4.5V were missing (at zero V) then that would explain why the "signal" at pin 10 seems to go nowhere. Or, if pin 6 (INHibit) is at logic high, then all analog switches would be disabled with the same result.