Window sash failure

So here's a new one. Dual (or maybe triple) glazed fixed pane window at my sister's house in Georgia. House is 15 years old, original windows. The other day all of a sudden the window starts to make crackling noise, and this happened. Can't feel the defects on inside or outside of the window. Interesting failure; not sure the cause.

http://www.windowsonlineuk.co.uk/blog/causes-double-glazing-crack/

Roy: Interesting article, thank you.