Encore CS6 - why are my menus showing wrong aspect ratio...?

Actually I do fades between menus and import them as .avi files.

For some reason Encore wants to display then a slight different aspect ratio.

This is despite right clicking each video file and Interpret footage > Conform to: SD PAL

I cleared the Media databse, I removed the .mpg m2v xmps files from the sources\Menus folder.   Argh.

Any ideas?

(I checked the imported avi files, they are 720x576 25fps PAL - look Ok when played outside Encore).