Here is an annoying one found when testing
UDIG-1660 - when working with the default DM Solutions WFS; two layers are shown "Parks" and "Cities".
When you go to edit the Style for these layers, the style page does not know what is going on (since it is a generic WFS "Geometry"?) and defaults to an invalid Mark (with size -1).
Now this would not be such a problem; set it up once the way you want it and forget? Except that this page is the default; and this "reset" happens everytime you open the style page (to toggle caching).
I am sad that uDig 1.2-RC3 went out with this bug; I usually test against GeoServer which is good about reporting back Point, Line or Polygon and thus did not catch this one.