iOS DownloadAndCache causes EXC_BAD_ACCESS

Simply using:

 using(WWW www = WWW.LoadFromCacheOrDownload(url,1)){
    yield return www;
 }

In a co-routine causes an EXC_BAD_ACCESS to be thrown in xcode.

In the xcode console it seems to download twice:

 starting www download: http://url.removed/beast/Crab-CQC-S0.unity3d
 http://url.removed/beast/Crab-CQC-S0.unity3d cached to /var/mobile/Applications/27731EAF-B7CA-4521-B2DE-9D5DF54B2142/Library/UnityCache/Shared/db74805771238a08bbdf6a1a77bc0b1c2f3f8d59
 starting www download: http://url.removed/beast/Crab-CQC-S0.unity3d

This problem only seems to occur when running on a device via xcode. Adhoc builds work fine.