When two constituents become spouses and are added to a household, users have the option to share contact information between the two individuals, on the Marriage Options screen. However, if a user chooses not to share a primary email address with the spouse when the relationship is created, future email addresses that are added to the spouse record and meant to be shared are not marked as primary, even if the new shared email address is the only one on the spouse record. Typically, if only one email address exists on a record it is automatically marked as primary.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.