Missing texture for jungle leaves.

Invalid.
Jungle leaves have the data value 3, not 11.

Try placing and breaking them again. there are 3 used groups of data values for leaves.
it goes oak spruce birch jungle - state
0 1 2 3 - normal
4 5 6 7 - no decay
8 9 10 11 - decaying
so 11 is decaying jungle leaves. I can only assume you obtained these in a much older version or in a bad snapshot, where silktouching or shearing leaves would give leaves with the exact data value rather than being mapped to 0/1/2/3.

So, they're invalid blocks. You'll also notice they disappear on placement.

This world has never been custom or seen a snapshoot. It is however quite old. Is this a conversion problem then?
Also, as per Conor McS's comment; Shouldn't there be a texture for decaying leaves?

Sound that this is caused by a bug in some previous versions. There were several jungle-leaves-decay-bugs fixed in 1.2 and 1.3.