Wow! After all this time I thought that you would at least know the answer to your question.   

Wokeh... here goes:

When you fire a flash, your camera meters your exposure of the subject based on the flash. Thus this will result in a properly exposed subject while disregarding the ambient exposure. Normally this ends up with the subject exposed properly but the background is dark - typical PnS flash usage scenario ler...

If you meter for the ambient and expose for that, the flash will then overexpose your subject.

So, when using flash you need to remember to balance for the ambient light. That's what sifu albnok always tells people. Don't just crank up your flash's power.

To solve the background dark issue, trying using a higher ISO and/or slower shutter speed to capture more of the ambient light. Your flash will expose the subject properly but let the slower shutter speed take in more light for the ambient and you will get a more balanced exposure overall.

When shooting under sunlight, adjust the flash power so that if will fill in the shadows but not overexpose the subject.

Like I always say - Get back to the basics and learn about lighting and aperture and shutter speed and what not and you will be able to figure all these things out by yourself. Fancy gears will do nuts to teach you things like these. No matter how many L or CZ or G lenses you have you will not be able to solve issues like this if you don't know your basics.