I see this on my Timecutter. The lines are just a result the of the physics of the clockwise spinning of the blades. They just shove everything to the right until there is no more further right. Both blades counter-clockwise spinning and the line would be on the other side, contra-rotating and there would be a line either in the middle or on both sides.
I have Gator Blades and the mulching discharge chute cover, and baffles. During grass season, the longer the grass the thicker the line but regardless, the lines of cut grass are finer chopped grass than without the mulching blades. The finer chopped grass breaks up easily with the next mowing or a rake for serious clumps.
On a side note, now that it's leaf season, the chopping is critical since I don't collect leaves but chop them where they lay. I did get some escapees on the chute side but a heavy rubber skirt has cut that to almost zero even on asphalt. Yes I get a line of finely chopped leaves on the right size but its not heavy enough to deter the grass growing in the spring and if It looks more thick than I would like, a second pass with the left blade over the line leaves no line. But leaves behave better than too long grass anyway.
