Just thinking of possibilities:

Are you sure it only rotated 1/4 turn? Not 1 1/4 or 2 1/4 etc,
as you previous test seems to indicate too much rotation not too little i.e moves 267mm instead of 50mm.

Also are you sure the leadshine driver pictured (1600 steps/rev) is the one driving that motor?
Could one of the others be driving it and have different microstepping settings?