Just searched for "curved" feather rather than "bent" which threw up broken feathers.....
To cut a long story short (the thread wasn't just about a bent feather) there were two people saying that their birds had over preened a particular or a few particular feathers so when they moulted, they appeared bent or curved.
This makes HUGE sense to me and what's going on with our Fred!
If you watch a bird preen, they pull their tail feathers into almost a C shape, yes? So, if Fred had something stuck on his feather one time, he could have pulled and pulled and pulled?
Also they were saying that their AV's said it was a behavioural thing (don't worry, there was other factors too so it doesn't have to apply to Fred) like swapping a toy in one persons case. I doubt he would have this with you, but maybe the previous owner.....?
To add the final piece in my mind (tell me if I'm wrong in fitting this together haha!) it would also explain Freds "tatty" feathers. If he preened due to a bit of unhappiness in his previous home, he probably says to himself: Meh, it'll be fine! And doesn't preen like he used to?
I hope to goodness that made some sense!!!!
I hope someone else with experience of this can help, if not Sharon, I can easily give my AV a call for some advice in the morning if you are still worried, no trouble.
I'm certain there is a simple reason for this!
Speak tomorrow, I'm sorry, I must dash now xx