@erickok looked into this and its very odd...
Basically

<details><summary>I have keys but no doors. I have space but no room. You can enter but can’t leave. What am I?</summary>
    A keyboard.
</details>

works as intended but your example doesn't. In your example, the list of children returned is

[TextSpan(" "), TextSpan(inherit: true, color: Color(0xdd000000), backgroundColor: Color(0x00000000), family: Roboto, size: 14.0, weight: 400, height: 1.2x), TextSpan(" A keyboard. ")]

I render the first item as the title of the dropdown so the empty text messes with it. In my example it returns

[TextSpan(inherit: true, color: Color(0xdd000000), backgroundColor: Color(0x00000000), family: Roboto, size: 14.0, weight: 400, height: 1.2x), TextSpan(" A keyboard. ")]

so the dropdown renders correctly. I'll see if there's a way to work around this.

@erickok can you check this again? I think I've solved it and hopefully prevented errors occurring in any edge case uses.

The title is showing now indeed, but in the center alignment something intentional?

I noticed that too, it seems this is only happening in your HTML because "A keyboard" isn't in a tag. If you use <p>A keyboard</p> then it goes back to the left side, I think this is something to do with the styling defaults.

Do you have an idea how I would fix this? There is a param on the ExpansionTile for crossAxisAlignment but I think hardcoding that might not go super well since someone might set text direction to LTR or an alignment to the right side.

@erickok Never mind... it seems that setting this parameter doesn't actually override the alignment if it is set for the tree itself. This PR should be good to merge now.