What's the point of having a move that blocks auto attacks when it doesn't even work?
Riot's spaghetti logic at work.
Blind's and Pantheon's shield also suffer from this pretty substantially. The blinds on Teemo and Quinn don't block on-hit effects, don't prevent CC from things like Xin'Zhao's AA-based delivery system, and they don't even block the bonus damage from certain empowered auto-attacks like Nasus's Q: while other empowered auto-attacks are blocked.
It's really difficult to know exactly what you're blocking and what you can't, even 5 minutes after reading the LoL Wiki article on what the fudge they do.
Ironically, pre-rework Fiora's Riposte also suffered pretty heavily from this: so Riposting a Teemo's AA would still leave you poisoned.
For whatever reason Jax's Counterstrike has been less susceptible to such spaghetti logic.
That said: one aspect of True Damage has usually been it completely bypasses any sort of defense: not just limited to armor and magic resistance, but also %damage reduction bonuses, Ninja Tabi, and %damage lowering debuffs like Urgot's passive as well as Exhaust.
Still: spell-shields, Zhonya's, and Invulnerability to still mitigate true damage.
That logic might also be applied to 100% evasion.
It might not.
LoL wiki isn't showing any info one-way or the other on their Dodge, Jax, or Shen pages and I don't care enough to keep checking.