Currently the spec says

If any of the grid items whose areas intersect the grid container’s first (last) row participate in baseline alignment, the grid container’s baseline set is generated from the shared alignment baseline of those grid items.

But actually this should be limited to the items participating in baseline alignment in that row, since a spanning cell could be participating in baseline alignment in a different row.

P.S. Also that should be “non-empty row”, to be consistent with #3645