In a new Superflat Overworld world, I placed down a track a couple dozen blocks long composed of powered powered rails and an activator rail in the middle. I had a cart launcher (launches carts off a wall when a button is pressed) at one end of the line and the other end was left open. I placed a couple dozen TNT carts on the same block (right-clicking on the very edge of the track) and I pressed the button and launched the carts. When the carts were moving, they were clumped together but not on the same block. The carts activated on the activation rail, traveled over the rest of the track then when they were ready to explode, they just stopped dead, the TNT was completely white and my whole computer lagged intensely at that point.
My computer took at least 12 minutes to completely recover, even after closing Minecraft about 7 minutes in. I then went back into the same world and nothing had happened and I was moved back to where I was before I launched the carts. I then placed down 2 TNT carts on the same rail and when I launched them, they just stopped dead past the activation rail on the powered rails, flashed white and then stayed white with minor lag. I then exited the world in fear of my computer lagging intensely again (which it didn't) but then my Minecraft froze (on the menu screen) and crashed. I've attached the crash report as an attachment. If anything is wrong, or you need more info, please just let me know with a comment and I'll do my best to accommodate. I'm sorry if this is a duplicate of any glitch, but I'm very inexperienced with this.