I have my player (sansa Fuze v2) set to "rewind after pause" by 5s. A very good feature for audiobooks.
If my Audiobooks are encoded at 64kbps stereo, 22kHz, constant bit-rate, then the "rewind after pause" rewinds to the wrong position, often several minutes out.

If my Audiobooks are encoded at 64kbps stereo, 44kHz, constant bit-rate, then the "rewind after pause" rewinds perfectly.
Bookmarking works perfectly, regardless of the frequency, its just the "rewind after pause" feature that messes up.