It is not a bug. It occurs if you enable the Remove Duplicates check box when adding files to the Xbench project.
If you check this box, ApSIC Xbench will consolidate all identical source+target entries in a given file into only one search result. The number of entries consolidated will be shown under the # column in the search results.
Therefore, Xbench finds 409 entries but displays 229 entries. If you look at the # column, the # column in the search results contains the number of entries that are identical in a given file.