Reseating deck belt on MTD mower

I pulled my MTD lawn tractor out this evening, intending to start mowing, when I noticed that the upper deck belt was off its path. My son just used the mower several hours prior to mow our back yard, which has me thinking that the belt came off between the time he finished mowing and the time I took the mower back out of the shed. Although it seems that the more likely time the belt came off would have been a week or two ago when I had the deck off to get the blades sharpened, but then I don't think the mower would have cut correctly. Anyway, I started working on putting the belt back on its path, and soon got rather confused. The belt is shaped with a narrow edge and wider edge. The pulley wheels seem to be designed for either the narrow edge or the wide edge. The "problem" is that the belt path has the narrow edge facing one of the wide pulley wheels. See diagram below.

Am I overthinking this? Are the pulleys not actually designed for a certain edge of the belt? Or is not that crucial that the belt faces the proper way on this particular pulley?

 

I believe that pulley was originally a V-pulley rather than a flat one, but it won't hurt the belt if it's a flat pulley and it works.

 

The back side of the belt should always be facing the flat pulleys, and the Vee part rides in the Vee of the other pulleys.
How long has it been since the pulley was changed?
Look it over for cracks or the outer band peeling off.
Belts drive from the center of the pulley, if it's resting all the way at the bottom it's worn out.

 

Consistent with Cheese' thought and Joe's explanation of v versus flat pulleys, I'm thinking that the flat pulley at the rear center position should be a v type, although it seems strange that the problem would have just suddenly appeared. Any chance that you removed any of the pulleys and possibly gotten them switched in the process? Take a look at all of them, including the lower ones on the deck; maybe they got switched sometime in the past.

 

I've never changed any of the pulleys myself, but it's possible the previous owner did. I've had it for about 5 years now. I looked up the part number this morning for the rear center pulley and the part number points to a flat pulley. Didn't have time to check the other pulley part numbers before walking out the door. Will check them all later today.

 

I compared all the pulleys to the parts diagram and they all appear to match up. I put the belt back on with the V side facing the rear center pulley and it seems to be working fine. I noticed this belt does need to be replaced though, as there are some definite low/worn/thin spots on the belt.