zenmp3 does not properly download long videos (50min)

zenmp3 does not produce a full *.mp3 from long videos (longer than 30min and so on). It's able to download the video entirely (as shown by the presence of a complete *.flv file), but the conversion process fails.

The GUI shows the message "Converting the song..." forever, but the conversion process gets stuck. I can state that because running ls -l in the target directory after a while shows that the *.mp3 file stops "growing" after a few minutes.

Output:

Your youtube-dl version: 2015.07.21
The data sent was:
https://www.youtube.com/watch?v=W6M_2xLwVx0
Allison Wonderland - Diplo and Friends mix.mp3
Fetching the song...
Converting the song...
^C^C

--> Song "Allison Wonderland - Diplo and Friends mix.mp3" was successfully downloaded to:
/home/vman/Downloads/

#1 zenmp3 does not properly download long videos (50min)