You can call it a bug or not but the simple fact is that I wasn't able to intervene in BoP's sub-biome assignments. They're simply out of my control. I honestly don't think even *they* understand that system (it has been dropped for the post-1.7.10 version) because they never fixed the South Seas Complex bug after over a year of complaints. I would have to write an entirely new sub-biome system and I'm not even clear what theirs is supposed to be doing.
ID = -1 has the same effect as incidence 0.
Snowy biomes will frequently generate next to any biome in the COOL climate. If you want to keep snow (mostly) away from any biome you have to take it out of COOL. To keep Forest and Plains out, reassign them to the WARM climate. (They are currently assigned to multi-climate groups that include them in COOL). That will leave you with very few vanilla biomes in the COOL climate, only Extreme Hills, (warm) Taiga, and Roofed Forest (which you might want to move too).
Roofed Forest, incidentally, is in there because I wanted to balance the biome assignments a bit. Vanilla puts it in WARM. I put it in there because I thought COOL climate was boring with only X-hill, Forest, Plains, and Taiga. If you're using BoP this won't be a problem.
WARM biomes will still occasionally generate next to snow in short stretches but it's fairly uncommon. This is due to a corner effect - the biomes are laid out in a grid and you can have "illegitimate" contacts at corners, which can expand to a short stretch of contact due to border adjustments.
I'll reply to CC questions either here, there, or on the GC thread. I prefer a CC-specific question be asked on the CC thread, though, to increase the archive value.