Pepega

Basically if you do a reload after certain events fire then the same event will fire 2 more times, this seems to go on indefinitely.

To test this for yourself:
1. Type /etrace in chat, scroll to the bottom of it.
2. Target something, see how UNIT_TARGET fires.
3. use /reload
4. open /etrace again and target something. Events have doubled.

This seems to atleast affect:
UNIT_TARGET, UNIT_FLAGS,UNIT_HEALTH, CRITERIA_UPDATE, UNIT_MAXHEALTH, UNIT_SPELL_HASTE, UNIT_ATTACK_SPEED, UNIT_STATS, UNIT_RESISTANCES, UNIT_INVENTORY_CHANGED,
UNIT_DAMAGE, UNIT_RANGEDDAMAGE, UNIT_QUEST_LOG_CHANGED

god save us all
-thanks ironi for pointing it out