Every Appy I've known is quirky... The one boarded here now likes to pretend it's opposite day from time to time, anything you ask, he will do the opposite (and the more people watching the more he plays it up)... It's not really a training issue, because most of the time he is a good horse, it's just something he seems to do to break up the mundane schooling activities.
My first mare was a excellent Houdini... There wasn't a single stall, paddock, knot or door she couldn't get open to escape... Though she rarely went far. There was one Day at a 4H show when she untied herself, and every horse there while we were eating lunch (and sneaky too... We were keeping half an eye on the horses)... Next thing we knew she had stampeded all the horses around the yard, then let herself into the gated picnic area and was happily eating the Zesty Doritos. :S
She would also go out of her way, if you weren't paying attention, to walk under low hanging branches when she was ready to go home while on a trail ride... She never did it on the way home, or in the beginning of the ride....
I own her son who is only part Appy... But he's got full Appy personality. He thinks he's funny... Steals things and runs with them (but only if you play... If you stand there and glare at him he'll drop it) he waits for an experienced rider to get good and comfortable, then starts popping in odd manuvers to see how well they fly (and more than one person has said they are SURE they heard him laughing)... He is normally very safe for beginners, but if you think you know what you're doing... He'll prove you wrong. He doesn't exactly buck, or bolt... But this odd little jumping dance paired with a good sprint, often from a completely solid "whatever you were doing".... His favorite is to lull a rider into thinking he's feeling mellow on the trail, pretending to spook (very little really spooks him) then putting in a hard deek to the left, and a bounce (always to the left). He then will stop and wait for the rider to get up, get on and will carry on like nothing happened.
I had another Appy colt who LOVED coffee... It just wasn't safe to set your mug anywhere near him, he could even get open the sliding tops on travel mugs..
Without spilling. He was also a gate latch opener... And a genius at untying himself.
Appies are the one breed that, as a whole, I'd say has more than their share of marbles rolling around in their heads...Though not always used for the most useful things... And memories like elephants.