M19 Spindle Orient currently (2.6.3, 2.7.0~pre2, 2.8.0~pre1) has some surprising behavior.
The issue was discussed briefly on IRC here:
http://psha.org.ru/irc/%23linuxcnc-devel/2014-10-29.html
We should figure out how M19 should behave, then make it do that, and test that it does that.