Merlin, I know this topic has gone relatively old but I suffered from the same problem, my model is KD-55X8509C. Ultimately I performed a factory reset, which seems to have corrected the issue.
If anyone still suffers from this issue you might try with a normal reset first, as factory reset also wipes out things like subtitle settings if using the TV as your receiver (and expecting the subtitles are streamed separately from video).
Those settings are found from Home -> Channel -> Digital Set-Up -> Subtitle Set-Up if using this model range and cable provider, Analogue Set-Up should be used for antenna households and so on. The documentation for the TV does not state where the setting is found.
