On releases with many mediums, the mediums aren't loaded until requested by the user. The colspan for the medium header is calculated on page load though, and at that time, if the medium isn't loaded, medium.has_multiple_artists always returns 0 (since the medium doesn't yet have any tracks loaded). That makes the colspan always 4 for those, even though it should be 5, causing a mismatch when the medium actually gets loaded and displayed.

Example for testing: https://musicbrainz.org/release/43481a1e-6271-4ee9-b5a6-6411c1895b68