It just seems to leak through the back of the LCD itself; not round the sizes.
I just tested mine with a VERY powerful (~50mW) green laser pointer, so I could try out different areas on the LCD. Pretty much anywhere on the LCD and down the exposure reading goes.
At ISO800, mode set to "P", I got 10s exposure with no light and 5 or 6 seconds with (A LOT!) of light.
I don't think it's a serious issue in real life. But I couldn't reproduce the behaviour with my 7D, though I didn't try very long, and didn't use the hella bright laser pointer for that.
When the lens cap is on and the VF cover is on, we are talking TINY amounts of light leaking to make the exposure reading change to 5s. Such a small amount of light would be TOTALLY AND UTTERLY swamped in any real situation, with a lens on. And remember, when the camera decides what exposure to use when the shutter is fired, it does so with the lens WIDE OPEN, before it stops down the lens and begins the exposure. So I think it would be hard to contrive a situation where the light coming in through the LCD would be anything other than negligible compared to the light coming in through the wide-open lens.