My new KD-55X9005C keeps locking up and is not responsive to any input from the remote control or the TV buttons. This can occur from anything from once a week to two or three times a day.

Sometimes it can happen shortly  after switching on (from standby) or after a number of hours of viewing.

The TV will display a picture and have sound but no commands from either of the remotes or the controls on the TV will work. (Even the on/off button)
The only solution we have found is to unplug the TV from the power supply and do a full reboot.
Ok, this does resolve the problem but surely it shoud not be necessary so frequently?

All firmware / software is up to date.

Come on Sony, for a TV costing just short of £2k I would expect it to be 110% in terms of operation