afaik, for WEP you should always be getting the HEX value of the key as the result, not the plaintext.

This is because different AP's handle the conversion from plaintext to actual key differently, so it cannot be reversed back to the plaintext from the decrypted HEX without using the same nonpublic method.

The HEX key will allow you to associate with the network, so the plaintext key isn't actually needed (even tho it would give more of an oomph value when demonstrating the vulnerability of WEP to someone).

Here's another site with a bit more explanation on the process for attempting to convert the HEX to plaintext:
http://latinsud.com/wepconv.html