I wasn’t able to play the PTR, but did anyone test whether the extra casts from tempering manuals affixes double cast behaved like regularly casting skill, such as proccing enchantments, unstable currents, passives etc?
Blizzard is not consistent when / if they use ‘cast’ wording (unstable currents, aspects, skill upgrades and enchantments are some examples)
this is incorrect. Leveled up a sorc enough to test this. They are not casts (for purposes of synergy with enchantments like frozen orb, or unstable currents which provide benefits on ‘cast’). They are simply extra projectiles part of one cast, so once again blizzard screwed up the wording on their tooltips or it’s bugged or both or they don’t care. I think what you might have seen was ‘confirmed’ was the bug that was fixed for season 4 launch, in that the explosions from frozen orbit counted as ‘casts’. It seems like one half of blizzard knows what cast means, while the other doesn’t.
Chain lightning ‘twice’ projectile is also incidentally bugged i found, when i tested this, and goes the wrong way, i would not play it until its fixed.
What do you mean “the wrong way”? Like you literally shoot lightning out of your butt? 
That would have been funny, but they just go out to the side instead of following the first ones like all the other spells do