Dissapearing ties

[Hernan]

In my first try with Lilypond (2.10.0), I seem to have met a bug that is driving
me crazy. A pair of ties randomly appears and desappears from the output (png o
pdf). 
Well, not really randomly, but small changes in the score (seemingly unrelated)
makes the ties to appear and disappear.
I produced a small test case, here is the source:

http://hjg.com.ar/varios/testcase3.ly

The missing tie is in the bass, first measure.
And here three outputs: first the original "bad" one, and another two that
result ok, by just changing the paper line-width, or the direction of a slur in
another measure. 

http://hjg.com.ar/varios/testcase3-bad.png
http://hjg.com.ar/varios/testcase3-ok.png
http://hjg.com.ar/varios/testcase3-ok2.png

Is this a known problem ?

Hernán J. González
Argentina