Garen Bug (again/still) am I just confused?

So, when ults and is spinning, I thought he was immune to magic damage. That's how it works most of the time. I lost a round last night because was spinning and after the spin started, ulted and chunked most of his hp. The veigar was actually 1 star and my garen was 2 star, if that matters. It cost me the round though because he took so much dmg. ult did the same thing (thought it was ability/spell dmg so garen should be immune to that while spinning also). Most times the spin to win works.. Not always though. Sucks losing rounds because of it. I mean, Garen kind of sucks if his spin doesn't work as it should. If I'm mistaken, he's even more meh than I thought.

Reporting though because I think it isn't working as intended..