How do I use protocol-relative URLs in IE9?

UPDATE

This was neither IE9 nor the plugin. It was the fault of the person using the plugin.

Original Question

I have an image at example.com/imag开发者_开发技巧e.png that I'd like to use in a Javascript plugin on both HTTP and HTTPS pages. The plugin currently sets the URL to

//example.com/image.png

Most browsers turn that into http://example.com/image.png or https://example.com/image.png propertly. When the page is viewed in IE9 over HTTPS, however, the URL gets turned into https:////example.com/images.png. That is, IE9 prepends "https://", not just "https:". How do I get IE9 to properly handle protocol-relative URLs?

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If you cannot find out what is happening then you can easily resolve the url's yourself by passing location.protocol + url to the plugin instead of just url.