A bit difficult to explain. I think I reported this during Beta3. It's like the invisible ship bug or it is the invisible ship bug but a little bit solved
Sometimes when a ship moves the icon of the ship stays and a new icon appears. This can happen several times during the same movement. If you're a little zoomed out (at the point where the 3d models are replaced with the icons) then no new icons appears but the 3D model is shown. In some cases the extra icon or 3d model doesn't disappear leaving a dummy ship (not really there just a picture)
Also if this starts to happen then most of the time when you move a ship it gets it movement points back if you use them all. EG, a ship can move 35 tiles and you use them all you can move it again 35 tiles and again.. and again.. and again.. Very easy to hunt down several enemy transports and other ships. I think it only applies to ships that have 2 or more extra engines but I'm not sure (most of my ships have either 2 or more extra engines or just the base movement)
Running on an AMD 4400 X2 + Geforce 7800