Spell Penetration for Infini-Spells

[Bunnysmack]

I've noticed it a few times in the past, but having actually compared the issue in RDI today, I can confidently say that spell penetration scaling with caster level is NOT properly working with mage infini-spells. I would cast anything from my spellbook at the giants there (the unwarded giants) and had 0 issues with spell resistance blocking my spells. I used my infini-castings of color spray, magic missile, and melf's acid arrow...and nothing seemed to stick.

The latter two are not a huge deal, as their damage is somewhat trivial for epic content, but color spray actually does matter, as that is some really reliable CC spam. Was this intentionally left out, or a bug?