Tested versions

• Reproducible in 4.4dev3, the web editor

System information

I'm running MacOS, Firefox, web editor

Issue description

After adding a new @export_tool_button to a script, all tool buttons break. Seems to be fixable only by reloading the entire project.

Steps to reproduce

My script:

@tool
extends Node

@export_tool_button("Hello world")
var hello_world := func():
	print("Hello world")

The button appears in the UI. When I click it, the error message appears:

The value of property "hello_world" is Nil, but Callable was expected.

"Soft reload tool script" doesn't help.

After reloading the whole project though, it works as expected:

Hello world

But add another tool button, and both of them break again:

@tool
extends Node

@export_tool_button("Hello world")
var hello_world := func():
	print("Hello world")

@export_tool_button("Hello world2")
var hello_world2 := func():
	print("Hello world2")

Now the first one errors with

Tool button action "<invalid lambda>" is an invalid callable.

and the second one errors with

The value of property "hello_world2" is Nil, but Callable was expected.

Reloading the whole project again, again, fixes both problems.

Minimal reproduction project (MRP)

Sorry I couldn't figure out how to attach the web project, and I running out of time right now.
It's basically the default project with just one scene and one script, that I pasted above.
I'm confident this will show up in any project.