Sivir's spellshield is not working properly

Various skills randomly go through and do damage even if you shield them. For example, sometimes Ashe's W will get shielded but do damage anyway. This especially happens against Yi. Some like Sona's empowered Q doesn't get shielded at all, I'm guessing it's coded as an auto attack, is that an intentional interaction?

Edit: To be clear about Sona's Q I'm talking about the empowered auto attack, not the bolt off the Q itself.