I'm afraid I am having the same problem on my Sansa E280. If I go into sound settings and select Bass or Treble and change it, all come back to correct settings including Volume. My current build is R17405.
In his code for R17274 he has a note:
* It's basically just a measure to make sure that audio does not clip during
235 * tone controls processing, like if i want to boost bass 12 dB, i can decrease
236 * the audio amplitude by -12 dB before processing, then increase master gain
237 * by 12 dB after processing.
It seems on the Sansa E280 its doing this at power down, but is not returning original settings after the restart of the unit. Is it something to do with the Sansa using the AS3514 Codec? Maybe.