The necromancers reusable parts passive reduces the resource cost of summoning skills by up to 50%. When the passive is active, and you are at low resources, you can not cast the summoning skill unless you have enough resources to cast the skill at its full cast. I.e. If my spirit guardian costs 4k magicka - 2k magicka with reusable parts passive, I will not be able to case spirit guardian until I have 4k magicka, even if reusable parts is active. I assume this is a bug, because if you allow your magicka to recover to over 4k in order to cast the spirit guardian, it would still cost 2k magicka.
This would great to see fixed please!