Cannot undo rename

When I tried to rename my item back like I used to do, only the first letter of the previous name. I searched for this bug and I wrote ''Rename'' ''Undo rename'' and ''Anvil'' and the bug I searched was not there. Please, I hope it's not a duplicate, works as intended or invalid. In the picture, I did that with a raw porkchop, but it does the same it every items like Name Tags, Spawn Eggs, Elytras and more.