[Graeme Dice]

I believe that the bug that keeps you from being able to cast a spell at a bonus site unless you have enough gems to cast the spell normally still exists. This shows up most noticeably when you find the Ultimate Gateway or the Oak of Ages. In these cases, when casting lichcraft for example, the spell will only be cast if you have 25 death gems, but only 12 death gems will be taken out of your inventory to pay for it.