Wow, I had the same problem and finding your post saved me. In my case the 720 footage was shot at 30fps. After import the video was about 10% slower than the audio so it rapidly drifted out of sync.
I thought I tried everything but I didn’t find the “Remove Advanced Pulldown” checkbox under the little gear icon, so thanks!
The FCP software team should be ashamed of themselves for leaving such a land mine hiding in there.
As far as I can tell, this setting is not changed by anything you set in Easy Setups or Audio/Video Settings. And I have not had the problem when doing importing before. Maybe what’s different this time is that I had to trash my preferences yesterday. If that is what caused the checkbox to be checked that means the FCP default for this setting is the way that caused the bad import. How do they justify that?