Podzol tilled becomes dirt

I attempted this in both survival and creative. Once I used a hoe on podzol with or without water, it would become normal dirt blocks. I am not sure if this is a bug or if it is intended.
I placed podzol beneath another podzol block and used a hoe on the top block. The bottom block regained the top texture of podzol, but the top block became simple dirt. I made sure to use a silk touch shovel for all of this.