#(override-auto-beam-setting ...) forces percussion staff?!

[Graham Percival]

This is a weird one.  Without the #(override...) function, this 
displays as
expected.  When I include it, I seem to end up with a percussion staff.
No clef, a single "staff line", and all notes on that staff line.
Fink 2.5.22-2

%%  setting the #(override-auto...) function reduces the staff lines to 
1
\version "2.5.22"
\relative c'' {
\time 5/8
#(override-auto-beam-setting '(end 1 8 5 8) 3 8)
a8 a a b b | c c c b b
}