The knobs on your M-Audio are probably assigned to the same function within the device. Certain numbers for controllers are reserved for MIDI CC, but the O2 already has built-in mappings that should work for most of its controllers within various DAWs, like Logic, Reason & Ableton Live. It's probably been reprogrammed...and not in a great way.
Here's how to fix this:
To verify the ID of a controller, move it so the number on the LED changes, then wait 2 seconds. The number that shows up on the LED display is the unique ID of the knob. If more than one of the controller is using the same ID, they will function like you suggested, as the same control.
Here's how to break them out into different unique controller IDs.
On the O2, select the 'advanced function' button, you'll see a dot following whatever the controller number displayed; this let's you know it's awaiting instruction. The keys are now awaiting data entry.
Then select your first knob. After the pause, this will display a number. The first C Sharp is the Controller Assign (it says ctrl asgn).
Using the Recall buttons to go up or down or simply selecting the numbers listed on the keyboard, select any number, and make sure it's unique from your other controller IDs. Hit the enter key. The dot on the display will go away, letting you know the data is saved to internal memory.
Repeat with all controllers, and then open your DAW to start knob twiddling! They will all now be recognized within your program, accessible for assigning as unique controllers.
For more in-depth knowledge, here's a link to the manual, spelling out this feature and many others.
http://www.m-audio.com/images/global/manuals/070404_O2_UG_EN01.pdf
:)