The rebound adjuster screws too far down, because the preload piece wasn't screwed onto the damper rod correctly.

Here's how it's done...or at least how I do it.

Wind rebound adjuster all the way out.
Wind rebound screw in 13 clicks (it won't bottom or anything so count the clicks)
Make sure locking nut on damper rod is all the way down.
Screw the preload assy onto damper rod until you just feel resistance. STOP! This is the rebound needle touching the damper rod orifice.
Wind up locking nut until it just seats. Finger tight.
Wind out rebound adjuster 2 or three clicks.
Tighten locking nut.
Check to see how many clicks of adjustment you have. To be honest, anything more than a few clicks out from fully in makes little difference.

Don't get all stressed if one fork has 12 clicks and the other 13. You could spend all day playing with it and it wont make any difference to the riding experience.

Maybe others have a different method......feel free to share.