The record of a “true” ID remains intact regardless. When someone disagrees with the originally suggested ID, the overall observation ID reverts to the lowest common taxon until a 3/4 consensus is reached for a lower taxon.
In practice, placeholder IDs are different from true IDs, though the distinction is often not readily apparent to new users. Others have expressed concern over misplaced placeholders (see Placeholder text and IDing Unknowns).
When possible, add a true ID instead of adding a placeholder. When a placeholder is needed, @Vireya suggestion is the best for the time being (until if/when the treatment of placeholders is changed).