Thanks Derek.
I found out more about the issue.
I originally tried the solution you offered by offsetting at capture but the result was 90% ok.
What I just remembered though is that the show I am working off was shot in PAL, then transfered to DIGi tae NTSC 29.91. However I came accross a lot of 1/2 field frames and replaced them with freezed flash frame.
And for some reason this is the 5% of recapture that didn't work.
But why isn't FCP recapturing freeze frame properly is a mystery.