Thanks! that shows what multiple checks can do. I can't find where I've put "The Scottish Folksinger" so I'll probably just replace that version of "Bonnie Lass Among the Heather" with "Queen Among the Heather" from "Till doomsday in the afternoon" - that's the one I hear people singing anyway.

The reason that BarFly missed that one is that it doesn't check the length of bars terminated with a double bar. This is because a double bar frequently comes before an anacrusis, and you'd get spurious errors. That's more or less what's happening in this example - the double bars mark line breaks in the text. That was a crude notational hack I got myself into for a while, back when some ABC programs had problems with staff lines that didn't terminate with a barline; I got the idea from old Scottish psalm books.

The other version has similar metre, though - the last bar of each line is extended, you could represent that either by a fermata ("H") or by a switch to 5/4.

Meanwhile, is this rewrite okay?

  X:0
  T:Bonnie Lass Amongst the Heather
  G:song
  S:Scottish Folksinger
  M:5/4
  L:1/8
  N:metre altered to avoid fermatas
  Q:1/4=88
  K:DDor
   FG |        A3 D D4 (EG)| G3   E   G4
  (EG)|[M:4/4] A3 A D3   D | c2 (BA) (Bc) d2-|d6
  (cd)|[M:5/4] e3 d d4 (AB)|(cB)(AG)  G4
  (AB)|[M:4/4] c2d2 A3   G | F2 (ED)  C2  D2-|D6|]

I try to avoid doing workarounds for bugs unless there's a really compelling reason - the little bugs you've found are presumably things that will be fixed in your next release.