The background is that both parts belong to different municipalities. Palombaia belongs to Tornimparte and Palombaia di Tornimparte belongs to the municipality of L'Aquila. The national statistical office istat lists them as separate entities.
Maybe better than to delete one of them would be to change them both to PPLX and create a new PPL feature which combines the two PPLX.
it's ok: there is no reason to keep this small village as two separate entities apart administrative boundaries.
You will find the same issue with [url=http://www.geonames.org/8948754/piattoni-villa-sant-antonio.html]Villa Sant'Antonio, split between Ascoli Piceno and Castel di Lama