Iron trapdoors are only breakable at one spot when facing upwards but turn downwards when redstone is placed 2 blocks under them

I placed an iron trapdoor to test out what it did (Seeing if it was like an iron door) and trying to find bugs and I did. I placed it facing sideways Like this:
"|_[|" the "[" is the trap door but on the opposite side was the only way I could break it. I placed redstone 2 blocks under (A block in between the iron trapdoor and redstone) and it made it close. I could just click on the iron trapdoor itself then to break it but then I made it go back up with redstone and a lever and it was like it had started.