It was related to if the string was already URI encoded. If we double escaped it setting that returned URL to the string as the source posed problematic to the processing of the URL.

I was testing this with an OGG file from archive but can't bloody find the original. Anyway, practical example....

```javascript
var uri = "http://test.com/something wee.mp4",
     parsed;

parsed = encodeURI( uri );

// http://test.com/something%20wee.mp4

parsed = encodeURI( parsed );

// http://test.com/something%2520wee.mp4
```