Inside the door mechanism (where the arm slides into the door) there should be two little rollers, about 1/4 or 5/16 in diameter, and the width of the slot. They have a tendency to pop out when the arms are not attatched to the pivots on the chassis. You might cross your fingers, pull off the door skin, and look down in the door for those rollers (there are alot of hidden little nooks in there, so look carefully). Pull the arm out from the inside, re-install the rollers, and re-insert the arm, being careful not to dislodge the rollers. They are nylon (number 6 I believe) you could use a thicker roller (nylon or similar) or possibly, you could use the same size or slightly smaller metal rods to make the door more difficult to accidentally shut. I'll try to measure mine, next time I'm in there (should be tomorrow or next day).
Hope it helps, and good luck.
PS. I'm going to try and fabricate a double stop arm, so I can open the doors straight back (stock/90 degrees) or ~120 degrees.