Darktable 2.6 - Sort by title not working at all (?)

I imported a few hundred TIFF scans (scans from negatives) into darktable. I edited their metadata, particularly the title of ALL of them, using a format starting with a long number, counting on the new darktable functionality to sort the lighttable view by Title.

Well, after completing adding all titles using the metadata editor, selecting Tltle as sort criteria: nothing happened. The images are still being sorted by FILENAME. Inverting the sort after selecting Title sorting produces the same output as inverting the sort while on FIlename sorting.

I tried selecting all pics then clicking sort and various other combinations - nothing happens. Using other sort criteria like “colors” (or filename) does produce a result.

Am I missing something or is this a bug?

Using DT 2.6 final from the ubuntu stable ppa.