It seems that the bds:prefixMatch has been replaced by a wildcard. You would now write this as:
# Search query.
PREFIX bds: <http://www.bigdata.com/rdf/search#>
SELECT ?subj ?label
?label bds:search "mi*" .
?label bds:relevance ?cosine .
?subj ?p ?label .
I have marked this as deprecated on the BDS interface, added a reference to this ticket, and added a reference to a correct example of prefix search on the wiki . I also updated the wiki page from bd: to bds:, which is the default namespace that is recognized for the search magic predicates (if you declare the namespace explicitly then it does not matter, but bds: is implicitly declared for search if it is used in query). Added some structure to the wiki page.
I have also updated the BD and BDS classes to reflect the movement of the search predicates from the BD class into the BDS class.
Thanks for bringing up this inconsistency.
Committed revision r7814.
 https://sourceforge.net/apps/mediawiki/bigdata/index.php?title=FullTextSearch (wiki page for search)