Minecraft tree generating issue?

I loaded a world on the old 1.2.5 version today, because I missed the old updates. When I loaded a world, all of the large oak trees seemed to be partially decaying or something - like the saplings started falling. The trees didn't disappear completely though. Does anyone know what the issue is?

What version of Minecraft are you using?

IT'S A CONSPIRACY! THEY WANT YOU TO UPDATE!