I've got an interesting bug. It only happens in PICO-8 itself. The bug can be reproduced with the following small program and reproduction steps:

function _init()
 menuitem(
  1,
  "switch weapon",
  function()
   --if (getthunder()==1) hwep=(hwep+1)%2
  end)
end

function _update()

end

function _draw()

end

Steps to reproduce:

1. Run the program.
2. Quit to console with ESC.
3. Type:

   x=10

   Any variable will cause the bug.

4. Type:

   resume

5. Press enter to bring up in game menu. Choose "switch weapon"

6. Observe crash. See image.

I reproduced this bug with a tiny cartridge, see the code in the OP.