I've just updated the modpack as FTB informed me an update was available. After updating and launching New World, and then opening my saved world in minecraft, I get this error in minecraft:
Forge Mod Loader has found ID mismatches.
ID 248 from MOD IC2 is missing
ID 473 from MOD Railcraft is missing
ID 249 from MOD IC2 is missing
I can chose to continue loading the game, and it seems to work ok, but of course I've not tried to use every single block in IC2 and Railcraft.
Not sure if it's useful to post this here, but thought I would just in case.