There is some kind of "tolerance" in SU when first something seems to be on axis but later it turns out that it is not the case. There are endless discussions about such seemingly minor issues but eventually they can become really bothering.
In the below file, there is a rectangle of 10m x 10m, edges set to display by axis. All is fine, the edges are red and green and if you PP the rectangle, the verticals will be blue, too despite one corner being just 0,05 mm higher than the others. There is not even an autofold line so SU definitely "adjusts" itself to such small differences.
I have to say that these "games" ar most popular on the Beta Forums and SU has been working this way ever since I can remember but we "refresh" these topics every time there is a new version.
Nilblo, never mind the critiques; these extreme, little things are that make discovering SU the most exciting thing (and also, plese, guys, be a bit more tolerant with others especially here in the Newbie Forum).