I use Clip Sport for Audible files, to be exact the external 16GB micro card (Sandisk Extreme HC 1).
At present 8 Audibles (downloaded in Enhanced/in its Entirety format) are contained in card.
Out of the 8 two of them displayed in incorrect length (1 for example 3 hours some minutes instead of approx. 45 hours).
Interestingly when this file is played back by WMP the correct length is available.
I've updated the player's firmware to 1.43 jus a few days ago.