The bug

If you use a flint and steel to ignite TNT, the in-game statistic for the number of times a flint and steel was used doesn't go up.

How to reproduce

1. Run the following commands to set up the scoreboard:

   /scoreboard objectives add flintandsteel minecraft.used:minecraft.flint_and_steel
   /scoreboard objectives setdisplay sidebar flintandsteel
   /scoreboard players set @s flintandsteel 0
   

2. Get a flint and steel, and set fire to a block. As expected, the scoreboard goes up.
3. Place TNT and use a flint and steel on it
   → The scoreboard amount doesn't go up, even though you used a flint and steel to ignite it