Using an E-PL7: yesterday, I was shooting indoors at a christmas party. Light was low, so I put on the kit flash (with a diffusor). I shot in aperture priority mode with the 40-150mm. Turns out that when I shot with a flash, shutter speed was even longer and my shots turned out blurry. So obviously I was doing something wrong; could anyone please elaborate what my mistake was and how to do it properly? Thanks!