Some time it hapens under the well developed roots of korean.actually the korean grass root system is the strongest among all lawn grases.if you are facing it then treat your lawn with good quality anti termite.one of my friend has a very good korean lawn but he was facing the same problem.he used Bayers Rengent.i think i have posted the product name earlier when you asked how to control termites.
Since termite problem of Korean grass has been discussed here so I will add my experience here. I live in Chaklala area, Rawalpindi. Termite spread in my lawn and we noticed it because of yellow patches appearing all over the lawn. We used to have few yellow patches on and off but that was mainly due to the dog we have. Another thing we noticed was the ease with which the grass would come off as if there are no roots. We also found few termites doing their work which led us to understand the exact problem.
Then I hired the services of a termite treatment company which sprawed the lawns with an imported medicine and then abundantly watered it. Charges were Rs. 5000 with 6 years warranty. 90% of the termite has gone away except for the green area outside the house where some of it is still there and would need another dose.