@manolito
I've just tested your suggestions.
And yes, the only halfway reliable workflow is repacking all your stuff into a mp4 container.
With mkv I've got scrambled/corrupted frames all over the place.
Mts/m2ts is fine in the timeline, editing ok... but the program just hangs at decoding/encoding stage.
No CPU, no HDD, no nothing
Exchanging both versions (32/64bit) to the latest ffmpeg binairies.
But same behaviour as far as I can see.
It's a shame, such a nice gui, and exactly what I needed.
Now back to search for a new tool....