I encoutered following quirk with the nightly.
On the minimap, each time a pixel update should be made (yellow dot moving) if the pixel is above the upped edge, instead of not drawing anything (since it's out of minimap), the game draws a vertical line of appropriate color across the whole minimap. This applies to both vehicle and the "removal" of vehicle (so the line color of the road or stop will also appear, at correct horizontal position).
The same happens for vehicles on the left of the minimap edge (horizontal line in this case). If the vehicle is beyond upper edge AND beyond left edge, it paints the whole minimap.
It looks like this (only vertical in this image):
(http://img391.imageshack.us/img391/8494/simutransmessedmap.th.png) (http://img391.imageshack.us/my.php?image=simutransmessedmap.png)
fixed in rev 2473. thank you for reporting!
Also isometric view was broken ... and should be fixed again.