when people get in groups, they often seem to speed up some songs...and drag out & slow down line endings on others. It seems to be some sort of attempt to 'push' for more feeling....hard to say. It can be very tricky to keep a song moving at it's proper pace. Shallo Brown is a pretty un-rhythmical song and needs a strong 'lead' to keep it moving..

(and trying to keep pumping shanties from being speeded up beyond any human ability to pump is a REAL trick!)