I've seen similar behaviour happen on a bug. I'm embarrassed to admit it was on SpeedMetal (yep, I finally tried the accursed map).
What happened was somehow a vamp or two were trapped outside the map (checked they were vamps in the spec mode after I gave up). Units in the viscinity of the confused place the radar dots thought they were (within the map) would simply fire straight up. From what I understand this happens particularly on SM, and particularly with aircraft (as such, one frequently sees flak firing into the air and coming down, wreaking havoc).
So we've found a good use for SpeedMetal: it's a wonderful stress test of the engine.
yeah, ive noticed it happens with all L2 fighters in AA. It appears when they get close to the enemy's defences ( fighters or anti-air) they going into loop of dodging and looping, and always gaining altitude.
I have found that you can only then select them by going to free cam view and lookign straight up and do a box select to catch it.
You can give it a move order, but it wont go as its stuck in it loop. Also trying to manually fly it down also has no effect.
The only thing to do is self-destruct it.
It is a wonderful way to destroy their base when their own shots fall back to earth :D
I'll do some more testing with it before I submit a bug report on mantis.
It's actually not useful in practical combat, extremely hard to aim - but it can still be used to good effect if you have ahem... a spam of units lined up.
Could also be used as a suppressive fire field, kinda like arty - only better =p.