That's the case of our cockatiel, Tcsh (for you computer nerds, that's "tcsh" as in the UNIX shell; we pronounce it "Teesh"). Tcsh is normally pretty darn smart for a cockatiel. One of the first things we noticed about him? her? was that he? she? likes to hold large pieces of food in his? her? foot, just like a larger parrot. (OK, I'll just call Tcsh a "him.") He seems like a serious, curious, and purposeful bird; it was his calm curiosity and purposeful (but silly) behavior that first got us to buy him at the pet store. In any case, Tcsh in general struck us as a brighter bird than our previous 'tiel, lovable old Torque, who was a social butterfly but not much of a philosopher.
The cage Tcsh normally lives in is a Hoei with doors that open out on top - something like upside down DeLorean doors. He had no problems with those, and would happily clamber out and, being the well-feathered bird he is, flap his way to the nearest human even with clipped wing feathers. We did notice he never came out of the vertical slide doors, even though he'd occasionally ride in through them while ravenously eating out of the food bowl/perch being placed into position.
However, this happy behavior changed when we took him with us on vacation. The temporary cage he lived in had only those vertical sliding doors. Once we got Tcsh in, he would not come out. Open doors meant nothing to him; they might as well have been closed. He'd do his let-me-out dance, and would climb onto our hands when we finally put them in the cage to coax him out, but the moment we tried to bring him to the door of the cage, he'd have a hissy fit and jump off. After a while of this, he got to the point of acting miserably frustrated and would just attack and/or run away from hands that came into the cage. He grew more and more stressed as the days went by, and getting him out was becoming seriously unpleasant. (And he was so happy and mellow when he did come out!)
It quickly became obvious that Tcsh simply did not Grok (Understand) Doors. He did not realize that the opened space in the middle of the cage wall was exactly that - open space he could pass through safely. And his inability to figure out how to otherwise get out of his cage was driving him batty - especially because (apparently) he thought us humans were trying to kill him whenever we brought him toward those evil non-existant Door-Things.
We tried various things - forcing him out, showing him the door, putting him back in - but finally we just wired the door open, left out some paper outside the door to lure him out (he loves chewing on paper - it's how we got him to perch on hands long ago), and waited. It took a while. Tcsh would creep up to the door and then run away. (Cockatiels aren't the bravest of birds....) Finally, though, he actually cautiously poked his head through, and you could practically see the light bulb go on in his birdie brain. "Ah ha!!! So this is actually a door!"
From then on, he would happily clamber in and out of the cage through the now-understood "door" thing, and was ever so much more mellow, relaxed, and pleased about life. He would also clamber onto hands and ride out through the once-hated doors. He was a changed bird. It was amazing. We just hope he doesn't learn to open those doors himself and get out of his cage like our lovebird.
So, just as young birds have to be taught what a food bowl and water bowl are, some birds need to be taught what a door is. It might just explain a bird's confused and psychotic behavior when it's in its cage. Good luck!