I know this is a really old post - but I am sitting with the same issue.
It is a backup GPT table that is causing the MBR environment to be read as if it is GPT.
The partition table scan identifies the MBR as being MBR-only and GPT data as being present.
The warning is innocuous - a false positive.
I am sure you have already resolved this - but just wanted to mention that these innocuous messages are best not fiddled with. - let sleeping dogs lie!