Trust no one: especially about SharePoint Search

Some days ago, the customer said he want to be able to search files in OneDrive using O365 search.
The solution is there: https://technet.microsoft.com/en-us/library/dn627526.aspx
After Step 5, i went into the search site, selecting OneDrive result source, and i run the search with no parameter... wow only OneDrive results; after that i tried another search with a word and... surprise surprise... results from everywhere.
After lot of hours of tentatives, the decision was to filter results again also in the query text of the search web part (path:https:// tenant_name -my.sharepoint.com/personal), in order to mantain mental sanity.