I'm afraid that this issue doesn't fall under those parameters. The captions come on and go off whenever the mood grabs them. We are on a ravine in the city with premium signal reception. In fact once on, if the mute button is selected, quite often the captions will go off. They seem to lead a life of their own independent of reason! I found someone else on line yesterday, also on their second new Toshiba, also with the same recurring problem.
I have lived here for over ten years, had Sony's and Samsungs all the recent ones with closed captions and none with this unique feature. We can select one of the obsure caption languages and the problem goes away (because no one is broadcasting in those languages in our area). However this is a ridiculous. The newer manual on the replacemet set hints at problems with the captions, but more about not being able to receive them rather than getting them when you don't want them.
So re the mute point, I'm afraid that doesn't trigger the appearance of the captions. It has to be either a software glitch, a defective component (used in last years model too), or a million to one coincidence that should motivate me to buy a lottery ticket!
Thanks for responding though!