I've noticed this problem a few months ago, and I'm also using the "parameter" setting. I think the semicolon is necessary for b2evo to distinguish between normal post URLs and tag URLs (let me check the code ;)).

//edit:

// Does the pathinfo end with a / or a ; ?
$last_char = substr( $path_string, -1 );
if( $last_char == ';' )
{  // ENDING SEMI COLUMN -> We'll consider this to be a tag page

inc/_blog_main.inc.php, line 160 (b2evo 2.4.2)

Maybe we should allow the user to change the semicolon to another char, but what if Google doesn't like the other char, too?

//edit: I added an option in my local b2evo installation. I think I'll patch my live installation and see if it works with a colon instead of the semicolon: http://www.webmasterworld.com/forum3/11070.htm (sigh, they want you to login... try [url=http://www.bugmenot.com/view/webmasterworld.com]BugMeNot[/url]).

//edit #2: Done. My tag URLs now look like "http://domain.com/tag:". If you know how to use diff files and want to try it (use at your own risk etc...): http://files.ax86.net/b2evo/seo_tag_char.patch. The patch adds an option on the SEO settings page (section Tag pages).

It works with a colon! :)
[url=http://image.gd/image,show,1,257133b195650105412bc62b3e00443915dce2b0,3]http://s1.image.gd/o/25/257133b195650105412bc62b3e00443915dce2b0.png[/url]

Works with a colon? I will try your patch.

Fplanque has applied a similar idea on the cvs version.

Great, thanks for the information. :)