There is a bug in the game that cause utility skills to go on cooldown right after swapping them in (video). The most consistent way I found to reproduce it is to use an elementalist. Have one of Ice Bow, Lightning Hammer, Earth Shield or Flame Axe, Glyph of Storms or Glyph of Renewal (my personal favorite because of it’s huge CD) as your third utility skill and Signet of Fire as your second one.
Now use the third utility skill and – if it is a conjured weapon – drop it after a few seconds. Next swap your second utility skill for Arcane Shield. Your second utility slot sometimes inherits the cooldown of the third one. It does not work all the time, but I have been quite successful at triggering the bug this way.