Here's the OP: http://www.linuxcnc.org/index.php/english/forum/40-subroutines-and-ngcgui/26290-subroutine-stops-without-warning
OP reports that it fails in 2.5 and works in master...
discussed on irc: http://linuxcnc.mah.priv.at/irc/%23linuxcnc-devel/2013-03-16.html
Related to bug #214? https://sourceforge.net/p/emc/bugs/214/