Pending Trips holds one row per PNR, showing the most recent change. When a new change arrives for a PNR that is already on the list, that row carries the new change.
Ignore works per reason. Choose Ignore this reason on a pending item and that exact change stays quiet on future scans, so a status you are deliberately leaving as is in the GDS stops asking for attention. An Ignored reasons panel on the PNR restores anything you dismissed.