I would exchange it, but I'd hate the hassle. I've seen warping in some cheap bezel plastic, but since this is the rear metal casing it's a bigger deal IMO. Something had to have happened to the TV before it got to you, even it works fine.
ht Panasonic TC-P60ZT60, Monitor Audio: Silver RX6, RX Centre, Radius 90HD; Martinlogan Dynamo 700, Marantz SR5006, PS3, Oppo BDP-103D
2ch Marantz PM8004, Sony BDP-S1000ES, JVC T-X3 tuner, Monitor Audio Silver RX1, REL T3, Apple TV, Peachtree Audio DAC•iT
lr Panasonic 50ST60, Sony BDP-S5100