Version details: gstreamer-plugins-mp3-0.8.8-0
Distribution/Version: Fedora Core 5 test1

I ran into this using sound-juicer for GUI and the gstreamer pipeline:
audio/x-raw-int,rate=44100,channels=2 ! lame name=enc vbr=4 vbr-quality=6

This I assumed would produce the exact same results as ripping with lame
directly, using the lame command line flags: lame -V6 --new-vbr

However, when comparing the files, there are some differences in the file
metadata. Most noticably, the track length in the gstreamer track is wrong and
keeps changing during playback. The bittrated is also reported as constant and
32 kbit/s, while the file size, compared with the track encoded by lame
directly, indicates that the track is in deed ripped at variable bittrated using
the V6 setting. 

Both files attached.