I've noticed a few threads on flyertalk that mentioned airlines changing seat assignments after ticket purchase and seat choice. This seems to result in a ton of unhappy customers and chaos when people board and try and shuffle back to where they want to be.

I assumed that if you chose your seat - and they didn't change the plane - that you would continue to get that seat. I've not noticed this happening on AC, but I also figured since you have to pay for your seat assignments on certain flights that they wouldn't move you. That said I have never really been picky about seat assignments so its possible that I never noticed - as long as I kept my window seat!

So, does AC do this? Is this a universal problem? Should I start checking my itineraries religiously?