When bundled Watchlist results (the "Group results by page" option is enabled) have a mix of seen or unseen items, the highlighted marker is not displayed as solid. Without expanding a bundle, a user does not see which changes are unseen.
Without highlighting, "Group results by page" option will display solid markers if any unseen changes are bundled with seen changes:
When highlighting is used, the marker for unseen changes won't be solid:
