The mana preservation focus isnt working with Chaotic Detonation. Wiz 2.0 focus Jaled's Flame Optimizer indicates 45% mana pres.
On avgerage the spell is costing around 1300 mana, base cost is 1800, which should take it down to 990 mana. Looks like it's only taking the 20% mana pres from focus items and spell casting mastery into account.
Checked with both Titanium and SoD client, also all custom files are updated on both clients.