I would say the first 3 chalk it up to not-so up-to-date currency conversion/rounding?

That expedia.com one I can't explain. I've encountered this kinda stuff too, which is why it's always worth looking. The biggest benefit to using the AC site itself is it makes changes including simple things like seating easier, interacts better with the app, plus you can use codes for discount/travel options.

But when using the OTAs you can also get routings AC won't necessarily offer. Yours in this case is easy, but I was going YYC-DFW-YYC and got offered a better and cheaper itinerary on expedia than on AC. AC seemed to insist I go YYC-YYZ-DFW rtn, but a flight that worked much better for me YYC-YYZ-DFW-IAH-YYC was on offer at expedia, so I went with it. I lose that extra bit of bonus points from the CC, but oh well.