does this also apply to Panasonic Lumix DMC-FZ38 using AVCHD Lite

I am trying to copy my old avchd lite hd movies stored in my Windows pc, to my new IMac but when I open them in IMovie they are double speed and normal sound. I am able to load and run new movies without any problem. The double speed only occurs when I copy an old movie back onto the SDHC card and then onto IMovie. Does anyone else have this problem?