Hi Fleetfoot, is it the same thing shown in this post here? :
http://moi3d.com/forum/index.php?webtag=MOI&msg=6875.59

It seems to be a bug in recent versions of Wine, looks like something to do with text anti-aliasing.

You could probably avoid it by using an older version of Wine, see here for some links to setting that up:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6875.61

- Michael