compile failure - "parsed object should be dead" in 2.19.20

[N . Andrew Walsh]

>I'm not top posting.

With a MWE:

\version "2.19.20"

\relative c' {
 a4 b c d 
}

I get the following error in the console output under frescobaldi:

Starting lilypond 2.19.20 [Untitled]...
Processing `/tmp/frescobaldi-NJlynW/tmpIzKobr/document.ly'
Parsing...
Interpreting music...
Preprocessing graphical objects...
Finding the ideal number of pages...
Fitting music on 1 page...
Drawing systems...
Layout output to `document.ps'...
Converting to `./document.pdf'...
warning: `(gs -q -dSAFER -dDEVICEWIDTHPOINTS=595.28 -
dDEVICEHEIGHTPOINTS=841.89 -dCompatibilityLevel=1.4 -dNOPAUSE -dBATCH -
r1200 -sDEVICE=pdfwrite -sOutputFile=./document.pdf -c.setpdfwrite -
fdocument.ps)' failed (256)

programming error: Parsed object should be dead: #<Grob NoteSpacing >
continuing, cross fingers
programming error: Parsed object should be dead: #<Prob: paper-system C++: 
Prob((Y-offset . 1.0) (system-grob . #<Grob System >) (staff-refpoint-
extent -3.776 . -3.776) (last-in-score . #t) (page-turn-penalty) (page-
break-penalty) (page-turn-permission . allow) (page-break-permission . 
allow) (vertical-skylines . #<Skyline_pair>) (stencil . #<Stencil>))() >

continuing, cross fingers
fatal error: failed files: "/tmp/frescobaldi-NJlynW/tmpIzKobr/document.ly"
Exited with return code 1.
-----------------------------
Error output is the same on larger files.

Cheers