It seems like the Oblivion Pickaxe's Curse of the Void enchantment does not function properly, as in blocks broken with the pickaxe are not destroyed. After some digging, this seems to be caused by Incantationem.

This is a known issue. Not sure which mod is causing it to not work though.

Not what is a conincidence. I tried to find out what mod causes it in this pack for like half a year now and just yesterday could drill it down to Incantationem, too and got it fixed.
Next version of Spectrum will have a fix, albeit Incantationem will have to do a tiny bit of work, too, to get their end working flawlessly.

Reference:
DaFuqs/Spectrum#46