No texture on top of potted cacti

I was playing a game of Minecraft in survival when I ran into a desert village. As I explored the buildings I noticed that the potted cactus without any textures on the top, (see first two images). So I hopped into creative mode and found out that the texture of potted cactus disappears when a slab is placed half a block above the cactus (see third image), which is how the cactuses I noticed where arranged in the village. Thankfully, this is a very small problem that I barely noticed, so no pressure on fixing it right away.