It happened to me in later game (just got Herakles), can not send interceptors to shoot down an UFO scout (reload game or restart computer does not help):
1 left click on UFO marks ufo with yellow circle
double left click moves the globe
1 righ click makes the yellow circle white again
2.5-dev May-15-2013
Win 7 64bit, q6600, HD6870, 4GB RAM