On maps that were created before the Update that changed the world (1.7.2), Taiga biomes had snow and thus should have been converted to Cold Taiga instead of Taiga to retain backward compatibility of the player's building environment.

Players who elected to build in snow now face global warming, rain and a melting world. This is a major annoyance in my case, I've seen the issue risen a few times, but not presented this way. The bug is not the lack of snow in the new Taiga... it's the eroneous conversion of the Old Taiga to the New Taiga instead of the New Cold taiga.