The upgrader will add a few filetypes. In the script I found these:

		$DB->query( "UPDATE T_filetypes
										SET ftyp_viewtype = 'text'
									WHERE ftyp_ID = 12
										AND ftyp_extensions = 'php php3 php4 php5 php6'
										AND ftyp_mimetype ='application/x-httpd-php'
										AND ftyp_icon = 'php.gif'" );

This is my list of filetypes:

http://www.blog.hemminga.net/B2evoforum/FileTypes.png

In the [url=http://demo.b2evolution.net/]Demo site[/url], which is basically a fresh install, I confirmed that there are mp3 things as file types by default:

http://www.blog.hemminga.net/B2evoforum/FileType2.png

So basically you are right. I have no idea what is going on. But it's not an error.

Good luck

This is the list that gets inserted for a new install:

	$DB->query( "INSERT INTO T_filetypes
			(ftyp_ID, ftyp_extensions, ftyp_name, ftyp_mimetype, ftyp_icon, ftyp_viewtype, ftyp_allowed)
		VALUES
			(1, 'gif', 'GIF image', 'image/gif', 'image2.png', 'image', 1),
			(2, 'png', 'PNG image', 'image/png', 'image2.png', 'image', 1),
			(3, 'jpg jpeg', 'JPEG image', 'image/jpeg', 'image2.png', 'image', 1),
			(4, 'txt', 'Text file', 'text/plain', 'document.png', 'text', 1),
			(5, 'htm html', 'HTML file', 'text/html', 'html.png', 'browser', 0),
			(6, 'pdf', 'PDF file', 'application/pdf', 'pdf.png', 'browser', 1),
			(7, 'doc', 'Microsoft Word file', 'application/msword', 'doc.gif', 'external', 1),
			(8, 'xls', 'Microsoft Excel file', 'application/vnd.ms-excel', 'xls.gif', 'external', 1),
			(9, 'ppt', 'Powerpoint', 'application/vnd.ms-powerpoint', 'ppt.gif', 'external', 1),
			(10, 'pps', 'Slideshow', 'pps', 'pps.gif', 'external', 1),
			(11, 'zip', 'ZIP archive', 'application/zip', 'zip.gif', 'external', 1),
			(12, 'php php3 php4 php5 php6', 'PHP script', 'application/x-httpd-php', 'php.gif', 'text', 0),
			(13, 'css', 'Style sheet', 'text/css', '', 'text', 1),
			(14, 'mp3', 'MPEG audio file', 'audio/mpeg', '', 'browser', 1),
			(15, 'm4a', 'MPEG audio file', 'audio/x-m4a', '', 'browser', 1),
			(16, 'mp4', 'MPEG video', 'video/mp4', '', 'browser', 1),
			(17, 'mov', 'Quicktime video', 'video/quicktime', '', 'browser', 1)
		" );

and the last snippet: the upgrader script where it upgrades to 1.8 Alpha:

		$DB->query( "INSERT INTO T_filetypes
				(ftyp_ID, ftyp_extensions, ftyp_name, ftyp_mimetype, ftyp_icon, ftyp_viewtype, ftyp_allowed)
			VALUES
				(1, 'gif', 'GIF image', 'image/gif', 'image2.png', 'image', 1),
				(2, 'png', 'PNG image', 'image/png', 'image2.png', 'image', 1),
				(3, 'jpg jpeg', 'JPEG image', 'image/jpeg', 'image2.png', 'image', 1),
				(4, 'txt', 'Text file', 'text/plain', 'document.png', 'text', 1),
				(5, 'htm html', 'HTML file', 'text/html', 'html.png', 'browser', 0),
				(6, 'pdf', 'PDF file', 'application/pdf', 'pdf.png', 'browser', 1),
				(7, 'doc', 'Microsoft Word file', 'application/msword', 'doc.gif', 'external', 1),
				(8, 'xls', 'Microsoft Excel file', 'application/vnd.ms-excel', 'xls.gif', 'external', 1),
				(9, 'ppt', 'Powerpoint', 'application/vnd.ms-powerpoint', 'ppt.gif', 'external', 1),
				(10, 'pps', 'Slideshow', 'pps', 'pps.gif', 'external', 1),
				(11, 'zip', 'ZIP archive', 'application/zip', 'zip.gif', 'external', 1),
				(12, 'php php3 php4 php5 php6', 'PHP script', 'application/x-httpd-php', 'php.gif', 'text', 0),
				(13, 'css', 'Style sheet', 'text/css', '', 'text', 1)
			" );

So... eh... I guess by 3.3.1 stable I should have those filetypes enabled? Because I don't:

css Style sheet text/css text
doc Microsoft Word file application/msword external
gif GIF image image/gif image
htm html HTML file text/html browser
jpg JPEG image image/jpeg image
pdf PDF file application/pdf browser
php php3 php4 php5 php6 Php files application/x-httpd-php text
png PNG image image/png image
pps Powerpoint slideshow pps external
ppt Powerpoint application/vnd.ms-powerpoint external
txt Text file text/plain text
xls Microsoft Excel file application/vnd.ms-excel external
zip Zip archive application/zip external

(sigh)