This does when watching via the humax as well as the Thomson which I have. I have a deprecate DVD player and don't have sky. Have had both hard drive systems for over a year and have had no problems, so am unsure as to why the tv is turning off, and yes I have a HDMI cable running from the tv to the humax but not the thomson.
Your television will automatically look for the next input source, like a tv aerial, or dvd signal if it loses the signal it is receiving. Disconnect everything else from the TV and only use the humax box to watch your recorded programmes, if it still does it then try replacing your HDMI lead (£6.00 at Tesco) Post back if if it does not work