"Tool button action "null::null" is an invalid callable" when using @export_tool_button

[GarrySlop]

Tested versions

Reproducible in v4.4.dev3.official [f4af820], v4.4.dev6.official [1f47e4c]. These are the only ones i tested.

System information

Godot v4.4.dev6 - Windows 10.0.22631 - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2060 SUPER (NVIDIA; 32.0.15.6590) - Intel(R) Core(TM) i7-9700 CPU @ 3.00GHz (8 threads)

Issue description

(I would leave a video but github didn't accept it)

I made a @export_tool_button in in of my scripts. It worked perfectly fine. Then i made another scene and tried to use it there. Gave me two issues.
Issue one was The value of property "insertVarHere" is Nil, but Callable was expected.(#97834), and the issue i am making now which is Tool button action "null::null" is an invalid callable.

In the Steps to reproduce section i mention that reloading the project worked, but that only worked in the MRP not in my main project.

Steps to reproduce

To get the error Tool button action "null::null" is an invalid callable you need to comment out the = funky and restart the project.
Then uncomment it and press the button.

To fix it reload the project while everything is uncommented.

Minimal reproduction project (MRP)

toolbuttonbug.zip

[timoschwarzer]

Probably related: #97834

[GarrySlop]

This may be related too: #98875