In functions.php line 455 the query string gets $db->quote'd which produces false SQL (at least for pgsql). I fixed this by removing the $db->quote, but this is ok only for me, since I run phpbt in a closed environment (not accessible from the Internet). Maybe a more elaborate solution can be found for the next release.
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There are several statements in functions.php (and maybe other places) where the argument to an IN clause gets $db->quote'd. Since the parameter to an in clause is not a string but an argument list, this will fail on any RDBMS.