I got a lovely piece of windelov that didn't like my tank and almost completely died - it looked like your browning off one. If it keeps browning off just leave the rooty rhisome bit where it is and if it isn't too unhappy it will slowly grow back. Mine has taken literally months but it is starting to speed up now.
So if you bought this recently and put it in, that might be what it is - either that or making new growth as above, but if it's a new plant I think might be doing what mine did.