Hi Nir,
You have incorrectly configured your material. At the top level you have a Multi/Sub-Object material, which has only 2 submaterials (accordingly MatID = 1 and 2). As a result, your leaves with ID = 3, assigns the material with ID = 1.
I added submaterials for Multi/Sub-Object, so it was 1,2,3,4, then clone your Leaf1 material to 3 and 4 slots. See my screenshot:
Also I attached the modified scene file...
Cheers
Small_Bush_GrowFX_2__1.max