Latest FTB update was rushed through (IMO), forge had issues and was not a stable recommended release. Optifine only updates for recommend versions of Forge only. So, optifine will not work with the current version of the mod pack. You need to update forge manually to 518 or more for optifine to work correctly.
Even C version will not work correctly with forge 515, pressure plates and the like won't respond correctly, you need to update forge.
Hopefully the next update to the mod pack will update forge and other mods that have bugs in them.