iPhone 4s iOS 6 intermittent screen dims and Ringer volume notification

Seem I am getting intermittent problems which look to be increasing in frequency.

One problem is the screen dimming as though I have turned the screen brightness down to minimum, with no apparent reason.

I've checked the brightness setting and it is set to my usual screen brightness, auto brightness is always off. Touching the screen or home button does nothing and switching apps has no effect either. No particular app is being used at the time so can't pin it down to a buggy app causing it. The only way to restore the brightness is to switch off the phone via the power button.

A similar problem is the dark grey square containing the ringer volume setting, set to the minimum one square appearing without touching the volume buttons. This stays on screen in a similar way to the screen dimming in that. Nothing apart from powering the phone off will remove it.

Also having problems with reduce volume button, could this be the cause of all these problems? This problem is when I'm reducing the volume it actually increases it to the maximum first before reducing it. Again it is intermittent.

Any one with same or similar issues?