When use slot, #key directive and transition together transition|local doesn't work

[MrWaip]

Describe the bug

I've wrapped Container in key directive in order to re-render it under certain condition and passed element with transition:fade|local in the slot. Tried to place span in another .svelte component and expected, that local transition would't be affected by parent's behaviour, but the glitch is still there.

It seems like the new instance of a component because of key has already been rendered, but the old one is still there, because of it has been hold by the transition

{#key key}
  <Container>
	  <span transition:fade|local>
		  Error example
	  </span>
  </Container>
{/key}	

Reproduction

Here is a reproduction:

https://svelte.dev/repl/f5de3baa974f4d4bb8f830e1e0b59e63?version=3.44.2

Logs

No response

System Info

nope

Severity

annoyance

[tohodakilla]

I wouldn't call it just annoyance, exactly this issue prevents me from having full page transitions in svelteKit on __layout.svelte level, so app that im making using lovely svelte instead of being absolutely beautiful (with transitions) is just beautiful.

[7nik]

The out-transition blocks umounting the whole block until transition ends so you temporarily get two components. It's written in the docs.
But there is a real bug #5950 - in the #key block a local in-transition isn't played at all.

[tohodakilla]

Yes you should get two components temporarily, but when I use #key + local transition isnt played and im left with two components (in my case SvelteKit - two pages being displayed at once) and they are gone only after refresh.