Is my new Nikon D3100 broken? too dark warnings in bright light

I've recently stepped up from a bridge camera (a Panasonic Lumix) to a Nikon D3100 DSLR. I like the camera in general but one issue is bothering me a lot and it is the exposure metering and a too dark warning.

Take today, a bright sunny day but cloudy, I was slightly squinting but then I work in front of a monitor all day. I’m stood in the garden with my back to the house and the sun is behind me and facing down the garden. I’m using the stock 55mm lens at 18mm. On auto mode, I focus on a tree at the bottom of the garden around 100 ft away, about 1/4 of the image contains sky, and half press the shutter – the flash pops up. I switch to aperture priority, check there is no exposure compensation, dial f7.1, iso 100 and half press the shutter to focus. The flash symbol and a ? in a square at the bottom right of the view finder start flashing and when I press the help button it says it is too dark. However, the speed the camera selected is 1/340th of a second! I tried all metering options and non made any difference. If I aim down a little so there is no sky no warning. If I aim up so I only get sky there is no warning.

Further experimentation showed I could cause the too dark warning very easily by focussing on a darker object in a generally bright frame. To some degree this makes sense to me although not with spot metering. I've even repeated this by focussing on a bright white object (a car) around 100 yards down my street with nothing in the foreground and it still issues a too dark warning on spot focus.

I have found Nikon support excellent so far (they've answered 2 Capture NX queries and problems I had very quickly) so I contacted them again about this and they basically say this happens with the D3100 and they reproduced it. They said:

"It appears the D3100 does not use the exposure meter to judge the requirement of the in built flash. It judges this in a similar manner to Matrix metering, taking all of the scene presented into account in both tone and light values and making a recommendation based on this."

If this is true surely at best it is a design fault. What do you think?

I'd love to hear from anyone else with a D3100 if they experience this too.