I'm sorry but we don't support ?v=x cases yet. In regular cases this should not be in URL. We'll take this under consideration in future versions. Please let us know, If changing of SERVER variable helps. We may add an option for this.

To make it work on my site, i just change line 242 in file "functions.php" after every update of wpforo:

old:
return $protocol . "://" . $_SERVER['HTTP_HOST'] . ($with_port ? $port : '') . $_SERVER['REQUEST_URI'];

new:
return $protocol . "://" . $_SERVER['HTTP_HOST'] . ($with_port ? $port : '') . (strpos($_SERVER['REQUEST_URI'], "?") ? substr($_SERVER['REQUEST_URI'], 0, strpos($_SERVER['REQUEST_URI'], "?")) : $_SERVER['REQUEST_URI']);

Issue still active in version 1.4.5

My solution still works (at least for me), just the line hast changed: Now it's in line 237

As far as I remember your website is very specific, it has ?a=b Get variable in each page URL. So will your solution also work on regular websites? Have you tested for standard permalinks?