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Adding new item, toggling an item, editing item's summary or recording reordering items in one window does not overwrite concurrent actions performed in the other windows.
Only the same action performed on the same item can get overwrittenoverwrites concurrent change, e.g., modifying the text of the same item in a different windowwindows.
Changes made in one window become visible in other windows when any checklist action happens in those windows (e.g., checking an item displays gets the latest version of the current checklist with changes from other windows).