Most likely it is the heat soaked engine and adjacent parts creating a "heat island" or pocket of recirculating, high temperature air during the times you have momentarily stopped traveling.
This has been reported on a number of different tractors and mowers (mostly zero turn units if I remember correctly).
The drafts of very hot air washing down into the grass has a blistering effect similar to a propane "weed scorcher torch" (if you have ever seen that).
While it is still covered by a comprehensive factory warranty you need to complain about this to Husqvarna.
There may be a factory bulletin or field fix regarding this issue.

The heat from the engine exhaust is causing it, my John Deere browns the grass .I just dont let it sit in the grass running ,I park it in the driveway ,next it will melt the black top, go figure.

Well, you can always cobble up an exhausr extension that shoots the exhaust up into the air--ala farm tractors.
You'd have to carry a tin can to place over the opening when it is parked, but you'd look like a real farmer whilst riding around on yer JD, or whatever you have!Ya might even be handy enough to make the real type of exhaust "flapper", like ya see on big trucks! ;0)

It only takes a few seconds to brown it , it will come back water it . Just shut er down in the grass.