Strange `free(): invalid pointer` on program exit after parsing XML.

[Steven Jeffries]

In my project, I'm using code to load a .tmx file (Tiled Map). Everything runs fine, but every time the program finishes running, I get free(): invalid pointer. I've finally tracked down exactly where it's happening and was able to make a minimal example, but I am stumped as to why.

require "crsfml"
require "xml"

File.write("test.xml", "<xml />") # just for the test case

XML.parse(File.read("test.xml"))

window = SF::RenderWindow.new
window.create(SF::VideoMode.new(400, 400), "Things")

window.close

If you remove the window bits, there is no error.

If you remove the XML.parse(File.read("test.xml")) line, there is no error.

Anyone know what's going on?