I was having some issues with downloading Asset Bundles in a project and realised they were happening because I had some test code that was giving the download the wrong CRC.
What's happening is the asset bundle is being downloaded, the CRC is failing (under the hood) and then the bundle is being downloaded again without any prompting. Only after this second download does the WWW throw an error and allow the download coroutine to end.
The code I'm using for the download coroutine is basically the example given in the Unity Docs with some error handling.
I haven't been able to find much of any documentation on this issue online. Is this a Unity or a WWW bug? Is it something I've done that's screwy? If it's intentional is there a way to prevent the double downloading?