That only works if the scale is -1 or 1, not 0.5. (-0.5*-0.5 = 0.25) It is more stable to use an abs function, I don't know the syntax for it in Max Script but in Maya you do; $scale = `abs $scale`; Abs, absolute value, returns a non-negative value.
Hey man, maybe you should just write your own Object Paint replacement ? I've done that as well, and I actually prefer it over the standard object paint... It's really not that difficult, I just got an example script off the net (Snap2Object.ms by P.G.Preeth). That way you have full control over the transforms of the…
sadly i don't know spit about max script (maya guy). so no working code solution from me. -1 is a special case which gives the inverse. @shawnolson so i took a look at that pdf and i'm going to have to say its crap for learning simple matrix algebra in order to understand 3d matrix transforms. its intended for math majors…