[Google Analytics +] Google Analytics pageviews not being attributed to mapped domains

Not sure how it took me so long to realize this, but when using the Google Analytics + plugin any pageview on a subsite with a mapped domain is not being attributed to that subsite, but instead being attributed to the root site.

When checking the subsites statistics via the wordpress dashboard /wp-admin/index.php?page=google-analytics-statistics&date_range=12 for example, no publically viewable pages are shown in the stats.

When viewing page views directly via the GA website, the pageviews on mapped domains show as being sub pages of the root domain, rather than a subsite.

This appears to be a problem whether I am using the retired wpmudev domain mapping plugin or "WordPress MU Domain Mapping" from the wordpress repository.

How can I ensure that pageviews are properly attributed to mapped domains and show up on those sites dashboard statistics?

My setup:

wordpress multisite

dashboard pages as original domain (unmapped)