AssetDatabase.CreateAsset randomly fails claiming object has been destroyed

I have started running into an odd error while building a series of asset bundles.

I create a ScriptableObject based asset using AssetDatabase.CreateAsset

Most of the time it works as expected, but sometimes CreateAsset fails with the following error:

 MissingReferenceException: The object of type 'ActivityBundleManifest' has been destroyed but you are still trying to access it.
 Your script should either check if it is null or you should not destroy the object.

where ActivityBundleManifest is the scriptable object class

I have checked the obvious things:

• The object has not been destroyed. I can print out content from it in the line before I try and create it

• Its OnDestroy method does not get called here

• The path is valid

• Unity is not running out of memory (using < 1GB, and system has 8GB free)

• The object is created using ScriptableObject.CreateInstance

I am using Unity 4.6.1 on OS X.

Does anyone have any clues as to why this is occurring?