waterlogged blocks wrong blast resistance

ignite the tnt.

what i would have expected: the tnt should ignite,blow up and not destroy any blocks since the center of the tnt is inside water wich has 500 blast resistance.

what actually happens: the tnt ignites,falls into the waterlogged blocks,blows up and destroys the blocks.

look attached screenshot

there is plenty more ways of recreating this i just show the most common ones