out-of-sync usually indicates wrong sample-rates.
you don't give detail of your your files, so general advice:
• best-practice: 48kHz/aiff
• convert before import to editor
• avoid 'formats' which allow VBR-encoding - such as mp3 ....
• avoid video with a diff. frame-rate as your project esp. iPhone material, which has a non-standard variable-framerate ( ! )
out-of-synch usually is noticed only on longer projects (>15-20min) … so, the average "Look, Mom, no hands!"/"cute, Kitty, Kitty, Kitty!"/"…paaaaarty!"-videos don't care for such details …
iM is meant as a consumer toy tool. so, it handles all kind of stuff, and does marvel, but there's some benchmark, beyond the simplicity results in errors.