Inaccurate audio length after conversion

[Reddelicious]

I am using the free edition to edit and convert some long wav files to mp3, but when I save them as mp3 files, the audio length is wrong. For example, the actual audio time of the file is 50 minutes, but it tells me that it's only 34 minutes, so when my media player gets to 34 minutes, the 'play' bar extends way beyond where it suggests it should, as the file is not 34 minutes, but in fact 50 minutes.

 

Help!!