Command /clear bug

Hello Mojang.

I'm here to report a bug with the command /clear in a repeat command block .

I don't want people have objects like TNT, firecharge, Lava ...
So, I want to clear those objects.

I use a repeat command block with Always active enabled.

I type my command : /clear @a minecraft:tnt

It's work, but only the first time, the other time, TNT disappear, but I still have the block icon in my inventory, but happily, I can't pose it (it's like if I was in a protect zone in a server).

I tested with other blocks or items, and the bug only affects blocks, items diseappered with the command, exept if I spam the item I want with Numpad key (for have the item in a particular slot).

To clear ghost blocks / item, I have to leave my server, and go in again, ghost items disseapered.

Is it possible to you to fix this bug for the next update ?

Thanks for your help.