Some blocks of leaves have "block.leaves..name" instead of correct ones.
Correct name: http://i.imgur.com/sJTtQIf.jpg
Incorrect name: http://i.imgur.com/XOtpbPa.jpg
This bug was in 1.6.4 Natura and still valid in the latest build of 1.7.10 Natura. Tested with Forge 1208.

Posted it to Waila bugtracker. https://bitbucket.org/ProfMobius/waila/issue/82/incorrect-leaves-names-in-vanilla-game-and

Never experienced it in Vanilla and other mods expect Natura. But maybe not enough testing...

Try growing a jungle tree and looking at the leaves. This is what I see:

It happens with all non-oak Vanilla leaves for me. I'm not really sure what could be causing it, but it seems like it'd be the same thing that causes this Natura issue (the .. is meant to have the Natura tree name in it, so somehow that isn't being set for some leaves).

It might actually be a Waila bug, I'm not sure.

While doing some unrelated testing, I found that this may actually be some sort of Vanilla bug, as Jungle leaves do something similar (Waila shows some of them as Oak Leaves yet they still render as Jungle Leaves). It seems to be more prevalent for leaves close to the trunk of the tree.