It seems that my Sql Server Full text catalog is not always up to date. I regularly run the script:
EXEC sp_fulltext_catalog 'HtmlSearch', 'start_full'
After that my catalog is up to date and my search results are fine. Is there somewhere an option that I have to set? And when does the full text update itself?
In SQL Server Management Studio, expand [Database Name] / Storage / Full Text Catalogs. Right-click your catalog and select Properties. Select Tables/Views on the left and check whether Track changes is set to Automatic.