I have been working with the ACS712 current sensor for awhile now, and am getting awfully bizarre analog readings. On all pins that have zero voltage applied to them, I am getting a reading of 1780-1900. That is, the Photon is simply plugged into a breadboard and nothing else is wired to any of its pins.
When you say all the pins have zero voltage on them, do you mean that you have connected the analog pins to GND? That would be unusual and could indicate a power supply problem or hardware issue.
If you have not connected the pins to GND or some other definite source and they are just floating inputs, then they will just read random values.