This can happen if you are logged into the management console (storage browser), possibly a locking/contention issue.
May be an issue if you add and remove buckets in batch scripts.
In particular this was happening to me when creating regionally diverse (non DRA) buckets :
gsutil mb -l EU gs://somebucket
Also watch underscores, the abstraction scheme seems to use them to map folders. All objects in the same project are stored at the same level (possibly as blobs in an abstracted database structure).
You can see this when downloading from the browser interface (at the moment anyway).
An object copied to gs://somebucket/home/crap.txt might be downloaded via a browser (or curl) as home_crap.txt. As a an aside (red herring) somefile.tar.gz can come down as somefile.tar.gz.tar so a little bit of renaming may be required due to the vagaries of the headers returned from the browser interface anyway. Min real support level is still $150/mth.