USA Campaign V7.1.1
Airplanes function rather particular when it comes to attacking units, facilities, or hexes in a tight space that is near an area where non proxy war entry is possible, such as ocean neutral tiles or neighboring countries. In this photo, you will see some of my tactical bombers in which do not want to take off from this airfield to bomb the nearby target.
If I send the airplanes inland, and then target the facility in question, the bombers will drop one bomb each and immediately return to base. They each have full fuel and supply loads and should in fact, orbit the target and blast it away.
In this photo, I have units taking off from Wonsan and flying to Hungnam to kill the last soldier there, and any targets around that hex. However, the units immediately RTB:

Check it out for yourself:
http://www.mediafire.com/?t402lxfd18hwrbe:edit:
after much testing, it seems that my planes do not like entering proxy war (north korean) air space.
:edit2:
Russia later declared war on South Korea, and China chimed in as well after South Korea randomly decided to war against Mongolia. I again tried to fly planes into China from South Korea, however, the planes refused to enter Chinese airspace, but did in fact, not RTB. However, my planes had no problem flying into the Russian Air space.