If a Set piece has spells and runs out of mana...

My tinker is wearing a full Tinkers Set suit with a Tinker Set Coif with Epic Bludge Ward and several other buff spells

Activation of a Set does not require mana to be in the item, or even have spells on the item.

I noticed that her skills were low so I scrolled up and saw:

20:08:56 Your Chainmail Coif is out of Mana.
20:08:56 Chainmail Coif cast Journeyman Armorer's Armor Tinkering Aptitude on you
20:08:56 Chainmail Coif cast Journeyman Swordsmith's Weapon Tinkering Aptitude on you
20:08:56 Chainmail Coif cast Journeyman Inventor's Item Tinkering Aptitude on you
20:08:56 Chainmail Coif cast Journeyman Arcanist's Magic Item Tinkering Aptitude on you
20:08:56 Chainmail Coif cast Novice Scavenger's Salvaging Aptitude on you

I took the Coif off, and then placed it back on


20:26:14 Chainmail Coif cast Novice Scavenger's Salvaging Aptitude on you
20:26:16 Chainmail Coif cast Master Armorer's Armor Tinkering Aptitude on you
20:26:16 Chainmail Coif cast Master Swordsmith's Weapon Tinkering Aptitude on you
20:26:16 Chainmail Coif cast Master Inventor's Item Tinkering Aptitude on you
20:26:16 Chainmail Coif cast Master Arcanist's Magic Item Tinkering Aptitude on you
20:26:16 Chainmail Coif cast Apprentice Scavenger's Salvaging Aptitude on you

It is still out of mana, so the Epic Bludge did not go on, but that is confirmation that the Set doesn't need mana to be used (as well as Set pieces with no spells on them)

So why does it drop your Set when you run out of mana?