Pushing TNT with a Piston and activating it at the same time duplicates it

**Expected to happen:
Then goes up and is powered by redstone torch.

**What actually happens:
And pull the lever, the tnt goes up and duplicates into 2 pieces of tnt only powering one.

Thanks for reading, hope this wasn't worthless information.I have attached two pictures of the glitch set-up and being activated.