If that texture is changed with others, transparent part of it turns black.
It is applied to every single texture pack.
Comments 2
This is a feature request and not a bug with the game. Judging by the resolution of other similar tickets such as MC-213852, we can therefore conclude that this isn't an issue. If you wish to post suggestions regarding the game, feel free to do so on the below links.
Official Minecraft Feedback Page - https://feedback.minecraft.net/hc/en-us
Minecraft Suggestions Reddit - https://www.reddit.com/r/minecraftsuggestions
Numerous blocks donvt allow transparency; in general, it's only blocks that have transparent parts by default, that allow transparency. This is not a bug.