When tags are set in the Search Engine service, if they are user-created tags, the search engine uses their IDs instead of their titles while searching, thus it's not able to work with the Lucene index, which always relies on tags' titles.

The problem can be traced back to the Generator: the form presents such code as:

<select id="tag-input-1" name="tags-1"><option value="ACCES_DIRECTS,INVISIBLE,FOOTER_LINKS,TOP_LINKS">- Tous -</option><option value="ACCES_DIRECTS">Accès directs</option><option value="INVISIBLE">Pages cachées</option><option value="FOOTER_LINKS">Liens de bas de page</option><option value="TOP_LINKS">Menu du haut</option></select>

Above is the HTML code for the drop-down list for tags used by the CMS, no problem here.

<select id="tag-input-3" name="tags-3"><option value="tag://0559d3dc-f6ab-4ac3-878f-014e982bd661,tag://20d78605-5942-471d-9799-7e701315a8e2,tag://cac7950a-5600-4298-96a1-fe2412e165f2,tag://e5d8801d-69d5-48cb-8a23-7e126d1fb39b,tag://6bc85226-24e8-4a50-94cc-f1367e8113cd">- Tous -</option><option value="tag://0559d3dc-f6ab-4ac3-878f-014e982bd661">Physique</option><option value="tag://20d78605-5942-471d-9799-7e701315a8e2">Biotechnologies</option><option value="tag://cac7950a-5600-4298-96a1-fe2412e165f2">Finance</option><option value="tag://e5d8801d-69d5-48cb-8a23-7e126d1fb39b">Modélisation</option><option value="tag://6bc85226-24e8-4a50-94cc-f1367e8113cd">Marketing</option></select>

Above is the HTML code for the drop-down list for user-created tags, with IDs instead of titles.