Seriously, what the fuck? I thought it was some kind of user interface glitch so I looked it up. Nope, they're A/B testing this shit.
Found this brilliant statement by Youtube on the matter:
Now note that we are deprecating one sorting option and that is by oldest video at the channel level. But don’t panic, you can still view the oldest video of a channel, by scrolling through it’s content’
Oh, yeah, just scroll to the bottom. Silly me, I guess I'm just a stupid idiot for not realizing the option was redundant since I can simply take the time to scroll through potentially thousands of videos.
Why are silicon valley tech people such freaks?
Also, Youtube's use of A/B testing is actually genius. See, normally A/B testing is just a method of determining how people react to a change by applying it to a test group and comparing their response to the control group.
But I've never seen an A/B test on Youtube that didn't end up getting rolled out to all users. No, the real reason Youtube uses A/B tests is to make extremely unpopular changes go down easier by limiting the amount of people they piss off at once.