[oblio]

They had a crazy vowel shift where vowels, which for example in Romanian are defined as sounds that "stand by themselves" [1] all became 2-sound things.

To make it obvious, I'll use the Romanian spelling for vowels, which is practically Latin (except for "ă" which is pronounced "uh").

A became ei.

E became i (ok, this one's the exception, but in practice it's still crazy, "Mercedes" manages to have 3 - three!!! - pronunciations for it).

I became ai.

O became ău.

U became iu.

So if you look at them, they're all 2 distinct sounds (ergo the 2 letters in the Romanian spelling, except for E, which is crazy enough anyway).

I'm not counting W, Y and such because I think they weren't used in Latin.

[1] I.e. they're need a single sound to be pronounced, don't need an additional supporting sound.

[qalmakka]

Without counting all those circumstances where A is still /a/, u is /a/ or a similar vowel, and so on. Basically, there's nothing that's still pronounced as it should :)