Gremlin doesn't draw the program extents correctly on lathes that are set up for rear tool post (DISPLAY, GEOMETRY = -XZ in the ini file). This bug was noted on the forums here: http://www.linuxcnc.org/index.php/english/forum/26-turning/24729-gangtool-setup--backtools?start=6
The attached patch fixes this problem.
Hmm... had to retract that patch. Should have a complete version later today.
Better patch is now attached. I would appreciate it if Jeff would take a look at this - it's my first foray into openGL.