So Well playing on my brand new 1.8.9 world I found a dense forest, it looked completely normal and awesome. I left the server (I am the only one able to go it so far) and I come back a few hours later aaaannd.....

That seems more like there was a fire rather than a bug. Although, we probably should disable lava lake generation in the biome

I couldn't find any lava lakes near by

Fire's really the only thing that could cause the trees to look like that, since if it was a bug with generation, there'd either be no trees/plants in a chunk or trunks/branches but no leaves (or the opposite of that).