OSX 10.9, Java 6
Creepers can be lit by Flint and Steels if they are held in the player's hand. If a creeper is placed in front of a dispenser with a Flint and Steel in it, it should function the same way, but it does not.
1. Spawn a creeper
2. Place a dispenser next to the creeper
3. Put a Flint and Steel into the dispenser
4. Power the dispenser. The creeper will be lit on fire, but won't explode.
The Creeper will light and explode, as it does when lit by hand.