It seems that Audition doesn't like VBR mp3 that were encoded with Xing. I have two of these files, and it thinks both have the wrong length: it thinks one is 40 seconds too short and the other is a minute too long. It is ok opening the one it thinks is too long, but the one that is too short, it does the same as you have experienced and cuts the end off it!
I can't find an input filter for AA based on the LAME codec. Although it's not very convenient, the only way I can find to open the files correctly is to decode them first with another program, such as
LameDrop &
LAME 3.96.1- which put in the same directory will give you drag and drop encoding or decoding