Had that happen with a used mower I had bought. Problem was curred with new blades--former owner when sharpening the blades was rounding the tips. I have also read where that can occur if the front of the deck is too high in relation to the back of the deck.

Maybe your deck alignment is off... If the blades cutting path does not overlap, there will be a gap between them that does not get cut. See sketch (this was posted a few years back, this board has a pathetic search engine)

{{gwi:326483}}

Worn blades, deck pitch can certainly cause what you are dealing with. Much of the time the issue goes back to a deck that is heavily caked w/ grass on the underside as well. More specific mower info may help.

what would cause a 25" mclane to do the exact same thing? my mohawk is about 3"

beyond above, excessively worn blades or incorrect length aftermarket blade(s)... or blade installed upside down.