Dispensers play the wrong sound file when lighting a fire with flint and steel.
The game plays the sound file for dispensers when they are "empty".
In other words, there are two sound files for dispensers. One for when they have contents inside, and the other for when they are empty. I'm saying that the game treats the dispensers as empty when it chooses the sound file, but the dispenser still uses the Flint & Steel.
If that makes any sense.
It is just a minor bug, but a bug none the less.
Comments

I cannot reproduce the issue and found this working as intended.
You will get the 'success' sound when you:
1) light tnt in front of the dispenser
2) set fire to the empty tile before it
If the tile is already on fire ... it will not count as either (nor will durability be used).

Found the issue: Once a Dispenser filled with flint & steel or bone meal fires unsuccessfully (there is already fire / nothing to bonemeal) from there on it will play the "unsuccessfull" sound file even when the action was successfull. It will do it until you reload the world.
Steps to reproduce:
1. Place a dispenser filled with flint & steel and a block which the dispenser can place fire ontop.
2. Activate the dispenser (successfull sound plays, works as intended)
3. Activate the dispenser while there is still fire infront of it (unsuccessfull sound plays, still works as intended)
4. Repeat step 1 and 2 anywhere else in the word. From now on every dispenser in the world filled with flint & steel will play the unsuccessfull sound even when the action was successfull

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Is this still a concern in the latest Minecraft version 14w08a? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Confirmed in 14w18b.

Confirmed for 1.8-pre2.

Affects 15w47c

Is this still an issue on the latest snapshot 16w44a?

Cannot reproduce in 1.11.2 with the steps provided by Tails.
Can someone else check and see if this is still an issue in 1.11.2?

Cannot reproduce in 1.11.2 either with Tails instructions
Confirmed.