AutoCAD Architecture :: Disappearing Cross Hairs

Every so often while working in LT-2010 the cross hairs will vanish from the screen but you are still able to pick items (as u move the mouse lines, etc hi-light in the usual way) also when you come outside the drawing area the mouse pointer will reappear (only while outside the drawing, in the command bars, etc)

the only quick way to return the cross hair to normal is to hit another tab & then re-enter the tab or model i was in. there seems to be no particular command that causes this glitch .