Ask HN:Facebook password behaviour: glitch or a feature?

Recently i found that facebook login methods have changed. I will try and explain with an example. Lets say, you have your password to be, "XYZabc123". Now, try and login with a slight change in the password, that is, "xyzABC123". To be more clear, change all the capital letters in your current password to small letters and vice versa. You can still login. I don't know if this just a added feature or a glitch. I have never come across this kind of situation, at least not on any other site so far. Or is it happening only to me?