Last week while i was returning to my shop,my van got smacked pretty good on the right side mldg and w/s,by an over-hanging branch.There they were,two cracks,one was about 3-4 inches and the other about 6-8 inches.Both comming out of the bottom of the moulding(plain as day).I was about ready to call my t.p.a.(oops)insurance to see if they had a vehicle that could come out to replace it.(i wanted to film them during the installation).However;and i have seen glass re-heal itself,but the lines would be a little noticeable,and you could always re-break it.Did gm come out with a new kind of w/s that we don't know about?Both cracks are gone(completely),as if nothing ever happened.Kinda cool.Missed out on the film,but saved my van.Never seen a break repair itself on w/s that gets pretty good abuse.

Not to doubt but more to play Devil's advocate. Maybe you just scratched it. Either that, or someone has some really fast service and you didn't see it being done.

I have seen heat close off a crack before, but never a crack that repaired itself.???

Not a joke.I've got my time in.I do know the difference between a scratch and a crack.I would not have brought this up,but i thought this to be very unusual.Plus the moulding is still dented where the branch hit it.Both were edge cracks starting from the same inpact spot.Even felt them with my finger-nail.I can't explain it either.But my bi-focals don't lie,they were there.Of course i don't really dare to pressure it either,just to see.

If I was to take a guess at it, I would definately go down the same road as CS. I would bet that the crack has just closed back up from stress. Heat will close it, but a crack will also close from stress just the same as it will open from stress. If you take a pick tool or blunt, pointy tool and GENTLY put pressure on the glass directly on top of the crack location, I will bet you will see the crack re-open. It shouldn't take much pressure at all if it is there. Do not press near the end of the crack where it would spread from, just the middle or at the edge.
That is my best guess because if it was there, I can assure you, it IS still there, just playing optical illusions with you.

I played around with it last night,using different light sources.If i put my nose up against the w/s and the light jjuuussttt right you can see it.I'm not so sure on the heat theory tho.We average only 3 days a year at 90 degrees(haven't seen that in 2 yrs).We may luck out on sunshine and get 3 straight days of it.
And it is nowheres near 90 degrees now(but it has been a balmy winter so far).No-way am i putting any undue pressure on them.You would think that going over frost heaves,wash-boards,pot-holes,A funky warm then cool winter,that they would have snapped by now.
Could be a good segment for the "mythbusters".

I guess that the angle of the crack(s) was just right to hide it from sight.