Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 18908)
+++ wp-includes/formatting.php	(working copy)
@@ -175,12 +175,12 @@
 	$pee = preg_replace('|<br />\s*<br />|', "\n\n", $pee);
 	// Space things out a little
 	$allblocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|option|form|map|area|blockquote|address|math|style|input|p|h[1-6]|hr|fieldset|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';
-	$pee = preg_replace('!(<' . $allblocks . '[^>]*>)!', "\n$1", $pee);
-	$pee = preg_replace('!(</' . $allblocks . '>)!', "$1\n\n", $pee);
+	$pee = preg_replace('!(<' . $allblocks . '[^>]*>)!i', "\n$1", $pee);
+	$pee = preg_replace('!(</' . $allblocks . '>)!i', "$1\n\n", $pee);
 	$pee = str_replace(array("\r\n", "\r"), "\n", $pee); // cross-platform newlines
 	if ( strpos($pee, '<object') !== false ) {
-		$pee = preg_replace('|\s*<param([^>]*)>\s*|', "<param$1>", $pee); // no pee inside object/embed
-		$pee = preg_replace('|\s*</embed>\s*|', '</embed>', $pee);
+		$pee = preg_replace('|\s*<param([^>]*)>\s*|i', "<param$1>", $pee); // no pee inside object/embed
+		$pee = preg_replace('|\s*</embed>\s*|i', '</embed>', $pee);
 	}
 	$pee = preg_replace("/\n\n+/", "\n\n", $pee); // take care of duplicates
 	// make paragraphs, including one at the end
@@ -188,24 +188,24 @@
 	$pee = '';
 	foreach ( $pees as $tinkle )
 		$pee .= '<p>' . trim($tinkle, "\n") . "</p>\n";
-	$pee = preg_replace('|<p>\s*</p>|', '', $pee); // under certain strange conditions it could create a P of entirely whitespace
-	$pee = preg_replace('!<p>([^<]+)</(div|address|form)>!', "<p>$1</p></$2>", $pee);
-	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $pee); // don't pee all over a tag
-	$pee = preg_replace("|<p>(<li.+?)</p>|", "$1", $pee); // problem with nested lists
+	$pee = preg_replace('|<p>\s*</p>|i', '', $pee); // under certain strange conditions it could create a P of entirely whitespace
+	$pee = preg_replace('!<p>([^<]+)</(div|address|form)>!i', "<p>$1</p></$2>", $pee);
+	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)\s*</p>!i', "$1", $pee); // don't pee all over a tag
+	$pee = preg_replace("|<p>(<li.+?)</p>|i", "$1", $pee); // problem with nested lists
 	$pee = preg_replace('|<p><blockquote([^>]*)>|i', "<blockquote$1><p>", $pee);
 	$pee = str_replace('</blockquote></p>', '</p></blockquote>', $pee);
-	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)!', "$1", $pee);
-	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $pee);
+	$pee = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)!i', "$1", $pee);
+	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*</p>!i', "$1", $pee);
 	if ($br) {
-		$pee = preg_replace_callback('/<(script|style).*?<\/\\1>/s', '_autop_newline_preservation_helper', $pee);
-		$pee = preg_replace('|(?<!<br />)\s*\n|', "<br />\n", $pee); // optionally make line breaks
+		$pee = preg_replace_callback('/<(script|style).*?<\/\\1>/is', '_autop_newline_preservation_helper', $pee);
+		$pee = preg_replace('|(?<!<br />)\s*\n|i', "<br />\n", $pee); // optionally make line breaks
 		$pee = str_replace('<WPPreserveNewline />', "\n", $pee);
 	}
-	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*<br />!', "$1", $pee);
-	$pee = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)!', '$1', $pee);
+	$pee = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*<br />!i', "$1", $pee);
+	$pee = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)!i', '$1', $pee);
 	if (strpos($pee, '<pre') !== false)
 		$pee = preg_replace_callback('!(<pre[^>]*>)(.*?)</pre>!is', 'clean_pre', $pee );
-	$pee = preg_replace( "|\n</p>$|", '</p>', $pee );
+	$pee = preg_replace( "|\n</p>$|i", '</p>', $pee );
 
 	return $pee;
 }