When holding items that would show both hands onscreen, such as maps, or thaumcraft 3's researches/thaumometers, etc, the left hand does not render in 1st person at all except for the outer layer. So far I've only tested this in 1.5.2, so unsure if it's an issue in other versions of old mc or not.

Here's an image of what that looks like, using a thaumometer.