Recently I’ve had an issue with the primary key on a Full Text Index. This SQL query was helpful in highlighting the primary key which was being used:
SELECT tblOrVw.[name] AS TableOrViewName
,tblOrVw.[type_desc] AS TypeDesc
,tblOrVw.[stoplist_id] AS StopListID
,c.name AS FTCatalogName
,cl.name AS ColumnName
,i.name AS UniqueIdxName
FROM (
SELECT idxs.[object_id]
,idxs.[stoplist_id]
,tbls.[name]
,tbls.[type_desc]
FROM sys.fulltext_indexes idxs
INNER JOIN sys.tables tbls ON tbls.[object_id] = idxs.[object_id]
UNION ALL
SELECT idxs.[object_id]
,idxs.[stoplist_id]
,[name]
,[type_desc]
FROM sys.fulltext_indexes idxs
INNER JOIN sys.VIEWS vws ON vws.[object_id] = idxs.[object_id]
) tblOrVw
INNER JOIN sys.fulltext_indexes fi ON tblOrVw.[object_id] = fi.[object_id]
INNER JOIN sys.fulltext_index_columns ic ON ic.[object_id] = tblOrVw.[object_id]
INNER JOIN sys.columns cl ON ic.column_id = cl.column_id
AND ic.[object_id] = cl.[object_id]
INNER JOIN sys.fulltext_catalogs c ON fi.fulltext_catalog_id = c.fulltext_catalog_id
INNER JOIN sys.indexes i ON fi.unique_index_id = i.index_id
AND fi.[object_id] = i.[object_id];
Code initially from here, but has been tweaked slightly.