\repeat unfold behavior

[Patrick Karl]

I discovered that the \repeat unfold 2 in:

\relative a' {
        \repeat unfold 2 {a' b c}
}

is not equivalent to:  a' b c   a' b c

but rather to:           a' b c   a b c

That surprised me.  I have not been able to find any documentation in Notation 
about this behavior.