Team fortress 2 question

It'll be probably fixed with the next update, don't worry.

Same for me

It's just a bug. If you sticky it to your UI as a pyro, you can see that it does track it.

for some reason it just dont show in the steam interface... it´s a bug... you can see it in the game interface

Yea I've got exactly the same - and with another one (medic healing I think [?]). It's a bug it is counting and will give you the achievement when you get there.

That bug has existed forever. Since that achievement existed, it has never read correctly.
Like NeonCore mentioned, you can track the actual progress in-game.

It's a counter bug in the stats page on the client. In-game if you see the achievement, your real stat appears correctly :)