Do a CTRL-A to select all, then type in "0" in the W field at the bottom left (shown in Ott's screenshot). You shouldn't have to change mode at all, it's just W values getting thrown off hugely, I find the easiest way is just to reset all verts to W = 0, it won't mess with any of your existing mapping and it's probably the…
Thanks for the tips! huh, why does max do that though? is there some hidden shortcut that throws certain vertex way up or down on the W? I ended up deleting and recreating the affected faces to fix it. but I'll remember this for the future.
I think it mainly comes about when using the "Best Align" planar UV mapping thing - possibly some way it calculates the mapping plane when it applies that throws off W values. I only ever notice this issue after using Best Align.
It happens with unfold mapping all the time. If you select all of the faces, right click, copy the vert data, and then paste the vert data, it fixes it as well. I find this slightly faster than zeroing all the W values because I don't have to move my left hand