The bug
From https://account.mojang.com/login, there is a link to register an account. From the link above, this can be accessed from the Register a New Mojang Studios account link.
This link take users to https://minecraft.net/en-us/store/minecraft/#register, which redirects to https://minecraft.net/en-us/#register. This is the homepage.
The correct link is https://checkout.minecraft.net/en-us/store/minecraft/#register. As you can see, the subdomain 'checkout' is necessary for this link to function properly.
A potential fix would be to automatically redirect users who stumble across https://minecraft.net/en-us/store/minecraft/#register to the checkout link.
This issue has been fixed in WEB, but still exists in MCL. The fix was to change the link given on the website to the correct link.