Two of Five encoders are giving identical values

[Analog]

We've got an encoder on every wheel and one for steering. We noticed that two of the five encoders return the exact same value. It is not a hardware issue, as we have isolated each one by physically unplugging them etc. It seems the software sees them as the same, even though they are declared and started separately.

In addition, we can 'control' which two mimic each other. Its always the first and the last in the code where they are declared. We verified this by rotating the declaration list, and sure enough, they followed each other - which further confirms that it has nothing to do with the hardware.

Any ideas?