You want to think of HDR as an exposure setting, that why it reverts back to normal.
You had it on your One X for still pictures, now you have it for film (video) as well.
In the following two images (on my One X), the first is without HDR, the second is with it. (Pixelation is from me compressing the image, not from the One X. You can see some picture artifacts from HDR if you know what to look for. If you don't, don't sweat it.)
When things are overcast - or when things are very bright and you lose detail in the dark shadows, as happened above - then HDR can help you.
In the second picture, I got a higher dynamic range of colors between the bright and dark places - hence - HDR.
You don't want to use it all of the time, but it's great when you need it.
Here are some great HDR shots from the HTC Rezound. Overcast day, but look how the colors on the train cars just *pop*!
I'm on the older phone, so - in your settings - do you still have one for aspect ratio/resolution?
That's where you'd set for highest photo quality.
And please notice - a 1080p big TV has far fewer dots than your camera at full resolution.
A 1080p TV has only 2 MP pictures.
That's been part of my argument against the megapixel myth for a long time.
Hope this helps!
PS - If curious, here's the fuller resolution pic of that train with an HTC enhancement filter applied - this was exactly what I had in mind when I shot it, I wanted to show a bleak scene with desert heat.