Prop value doesn't stay default if it gets undefined

[elite174]

https://svelte.dev/repl/d8c112a251984339b564f0506365e32f?version=3.6.7

It seems like default prop value is used only once (after the mounting), and it doesn't work after that.

[antony]

This appears to work exactly as intended.

I think you are mistake the initial value of a prop for the "default" value of a prop. This isn't the case, it's just an initial value. If you set the value to undefined, it doesn't default back to it's initial value.