Fixed in 1.5.1
Same issue as Bug #1146.
The fighter’s Quietus seems to have rather erratic behavior when it comes to mana. For starters, the in game journal says, “Fueled by red mana,” even though the weapon uses blue and green. When Quietus is swung, it is supposed to use 14 blue and green by default (assuming a charisma stat of 10). Yet if the player has an uneven amount of blue and green mana, like more green mana than blue mana, Quietus will keep firing even after it uses up all the blue mana, and continue to use green mana at the normal rate.
An example of this: I had 20 blue mana and 50 green mana. Quietus fired twice, using up all my blue mana (even though it should have switched to its unpowered state after one swing) and then fired twice more, using up all my green mana.
When all blue and green mana is consumed though, Quietus can still fire, except it will use no mana at all. In other words, it can fire indefinitely without losing power.