KX indoor low light exposure differences w/ 2 lenses

Hi,

Below are a couple pics taken with my KX to experiment w/ exposure a couple different lenses. The brighter using a Sigma 17-70mm f/2.8-4.5 and darker with a Sigma 10-20mm f/4-5.6. The pictures were taken in Program mode, AWB, auto ISO 200-3200, matrix metering, center focus, exposure not tied to focus point, no exposure compensation.

Why did the camera choose such a brighter exposure with the 17-70? It does not reproduce the actual scene (the room was dimly lit--we were watching a movie). Further when shooting with the 17-70 the KX chose the widest aperture possible the exposure using the 10-20 is stopped down.

I've shot mostly with the 17-70 since getting the KX and the exposures the camera thinks is correct (whether program, Av, Tv, manual) seem to come out quite bright for indoor low light scenes.

Any helpful feedback would really be appreciated. I'm puzzled.

Sigma 17-70: 19mm, f2.8, iso 3200, 0.5sec, program mode

Sigma 10-20: 20mm, f6.3, iso 3200, 0.25sec, program mode