Hey Peter,
We're working on fixing this and will have a better answer soon, but I didn't want to continue to leave you hanging.
The build status you see on the site is pointing at the tip of tree, which is a lot less stable than what we release. Occasionally there are testing infrastructure bugs or chrome bugs that keep some of the tests red, but we know about them and ignore those false negatives when we release, even though the matrix will show red. Any single test, including one false negative, is currently reflected as red for an entire portion of the matrix.
This makes that particular build status useful for us internally (sort-of), but not for your purposes. We're working to change that so it more accurately reflects the release status and stability, but it will take a bit to accomplish.
-Matt