Beams not drawn after \unHideNotes

[James Harkins]

I'm making that exercise for my students now** and found... the first group 
of eighths after \unHideNotes is missing its beam. It omits 8th-note flags, 
and it draws the stems as if it's going to beam them, but... no beam.

** Thanks, Pierre, for reminding me about \hideNotes!

\version "2.18.2"
\relative c' {
 \hideNotes \repeat unfold 6 { e8 }
 \unHideNotes
 e8 f8  % beam is not drawn here
 g a g2.
}

If I explicitly beam, it works. But I think I shouldn't have to.

\version "2.18.2"
\relative c' {
 \hideNotes \repeat unfold 6 { e8 }
 \unHideNotes
 e8 [ f8 ]
 g a g2.
}

I think I see why... it's trying to beam a group of four 8ths, where the 
first two are hidden. It'd be nicer if LilyPond could detect the situation 
and just Do The Right Thing.

Par for the course today... just about everything I tried to do on the 
computer today required a bug report :(

hjh