Piece of my drawing gets erased when I undo

[languid shore]

It's in the name
How do I fix this

[loud skiff]

it isnt a bug

its how undoing works

[languid shore]

I only copy and pasted both parts but when i undo the part it erased

[random yacht]

That's what undoing does, it goes back a step. If it goes more, check your screen for damage