Ok, *Assuming* for a minute that there is an obscure bug in the coefficient calculation, it's quite possible that it's an integration bug eg:

The player thinks that one range of values is valid.
The DSP thinks that a different (lesser) range of values is valid.

Now for the most part, this kind of bug isn't apparent in everyday use, as most values fall in the DSP's range. But once you try to extend beyond that range then the value that you give the DSP isn't 'valid'. In the way that the eq sections are implemented in the DSP, I can tell you that one word (16 bits) appears to control gain, Q-factor and the 0/-6dB scaling. So it is possible that if there was a bug of this nature, then it would be possible that an invalid Q factor may very well affect the gain...

With all this sheer speculation in mind, take a look at band 4. Try reducing the Q factor to 5 and see what happens.