Once generating a taiga hills biome, grass colour and the trees appear to be "not there".
I have tested this on a server and the trees are really not there! There are also lighting issues with the trees (I can imagine, I am a C++ programmer).
Just create a world or custom one to spawn in a taiga biome. Look at the mess.
P.S. This bug also appeared in taiga biome. I just moved a little and F3 and it aid taiga hills. The tags biome glitch is also shown in the F3 screenshot so I figured pointing that out.