Many of my tower locations when you mouse over them have a location showing as - instead of an actual location. Some do give a generic location.
I assume it is taking the location from one of the first AP's assigned syslocation ? Does it have a preference or is it the first added?
I am considering the fact that you have put the correct co-ordinates while creating those towers in the cnMaestro. Also, you can set the AP co-ordinates as well.
Do you have any screenshots which you can share?
If you go to to MAP (the large version) the Tower locations will show - as location even though there is a syslocation in the AP's and gps coords are correct.