When dynamically injecting script elements with async explicitly set to false, if you insert 2 script nodes with the *same* src which 404s, the next script with a valid (200, 304 etc.) src hangs, and does not invoke the onload listener.
Test case is attached.
This impacts YUI's Get utility, which is used to dynamically include scripts to the page. We use the DOM0 onload and onerror listeners, instead of onreadystatechange, because we need to identify error and success cases for loading (since it's a generic utility, we can't check for something which the scripts may be adding). Also, I believe there are some use cases where onreadystatechange doesn't reliably indicate "interpreted", only "downloaded".