Metadata size is reporting wrong values in the membase vbucket backend stats

Hi,

I have a cluster of 6 nodes with 2 buckets. 1 bucket is memcached and the other is membase. The membase bucket uses 11.7G of RAM in total. In the backend stats I see there are 4.5M entries or 9.0M in total (with replica) but I only have 25.5M or 51M in total of metadata? In the sizing guidelines I see that the metadata is already 150bytes, which totals up to 1.5G of metadata (9M keys x (150bytes metadata + 33bytes keysize) x 2). How can this be? Is there an error in the backend stats?