TNT Visual Glitch When Dispensed into a block

When TNT is dispensed into a block it will appear as if it is on top of the block for a quick period of time
*note I have found this happens with any block with a hit box at least 1 block high, so any normal block, ironbars, fence, netherfence, walls, ect

What I expected to happen was the tnt to fall below the block into the water

*What actually happened was the tnt did fall below but for a few frames the tnt appeared as if it was above the block quickly even though it was below

Steps to Reproduce:
1. Place a dispenser with tnt in it and a button on it facing into a block, fence, ironbars, wall, ect
2. Place water under the block, bars, fence, ect so the tnt doesnt blow up the entire machine
3. press the button and quickly the tnt will appear as if it is above the block even though it is below

I have attached a video to demonstrate the effect
*note in the video I used ironbars, however this also works with other things that I mentioned before.
also I have slowed down the video in the 2nd half so you can clearly see the tnt above the block