Error: Deleting persistent object without writing it first

Since I’ve updated to Unity 2.6.1 (pro) im receiving the following error:

It seems that have no other effects than filling my console, but I wish to know why this message is being showed… Anyone knows?

Thanks in advance.

Agree, I have the same problem even if I run the sample project of “AssetBundle”.

Does this only seem to happen when you use AssetBundles?

Yes,
but ive seen some topics about this…
It seems to be just a warning masked as “Error”.

I got the same problem, any explanation from official?