It's a defect. Check to see if they have a firmware update and if that doesn't cure it, call it defective then return it for another model.
I have a philips 47pfh6309 tv and i have a problem with playing movies from usb external hdd or stick. Sometimes, randomly, usb disconnects and the source changes to the last used source. If i go back on usb, it disconnects again. I can't do anything but to wait a few minutes. Then it works. This happens randomly. Sometimes i watch 5 hours of usb movies and works fine, sometimes it crashes after one hour of movie.
I tried an external hdd and a usb stick, i have the same problem with both.
First i thought it's because of the video file, but after it first disconnects and i go back on usb source, after a few secconds it disconnects again while i am in the menu, not playing any video.
Because it happens randomly, i'm afraid that if i send it in service they will say the problem isn't present.
Do you have any ideea what could i do?