Workaround solution from https://www.sony.co.uk/discussions/thread/148682 -
Sony KDL-32CX523 shows prompt in the middle of the screen:
This event is available in HD on service 935.
Do you want to change to HD event?
[Yes] [No]
Select [Yes], and it goes to channel 935.
Unfortunately, channel 935 has no signal - the real BBC One HD signal is on Freeview channel 050 - so that isn't a good result:
Workaround is to delete the relevant channels from the TV.
To delete channels, go to
Settings/Home Menu > Digital Set-up > Digital Programme Sorting.
Here, we've deleted "BBC HD" (934) and "BBC One HD" (935), and we're about to delete "ITV1 HD" (936) and "Channel 4 HD" (937):
The channel numbers we got (934 - 937) are different from those seen by abarton (833 etc). Maybe it's region-dependent. We're in a BN16 postcode.
Sometimes we've seen it switch to BBC HD correctly when you say [Yes], which means that if you want to be sure of not getting those "change to HD event?" prompts at all, you may have to sacrifice the HD channel. That's kind of a shame - somewhat defeats the object of having an HD set.
To be notified if Sony do something to fix this - and to encourage them to fix it - select 'Notify Me' at:
Bravia : On screen broadcast message prompt, change channel to HD option ?
http://sonycic.custhelp.com/app/answers/detail/a_id/1878/