Index: src/wp-includes/formatting.php
===================================================================
--- src/wp-includes/formatting.php	(revision 34809)
+++ src/wp-includes/formatting.php	(working copy)
@@ -1794,7 +1794,7 @@
 	// WP bug fix for LOVE <3 (and other situations with '<' before a number)
 	$text = preg_replace('#<([0-9]{1})#', '&lt;$1', $text);
 
-	while ( preg_match("/<(\/?[\w:]*)\s*([^>]*)>/", $text, $regex) ) {
+	while ( preg_match("/<(\/?[\w:]+)\s*([^>]*)>/", $text, $regex) ) {
 		$newtext .= $tagqueue;
 
 		$i = strpos($text, $regex[0]);
@@ -1871,7 +1871,7 @@
 				$tag = '';
 			}
 		}
-		$newtext .= substr($text, 0, $i) . $tag;
+		$newtext .= str_replace( '<', '&lt;', substr($text, 0, $i)) . $tag;
 		$text = substr($text, $i + $l);
 	}
 
@@ -1879,7 +1879,7 @@
 	$newtext .= $tagqueue;
 
 	// Add Remaining text
-	$newtext .= $text;
+	$newtext .= str_replace( '<', '&lt;', $text );
 
 	// Empty Stack
 	while( $x = array_pop($tagstack) )
Index: tests/phpunit/tests/formatting/balanceTags.php
===================================================================
--- tests/phpunit/tests/formatting/balanceTags.php	(revision 34809)
+++ tests/phpunit/tests/formatting/balanceTags.php	(working copy)
@@ -204,4 +204,34 @@
 		}
 	}
 
+	/**
+	 * @ticket 22625
+	 **/
+
+	function test_encodes_lone_anglebracket() {
+		$inputs = array(
+		    'This is < That. <blockquote>foo</blockquote> Text <a href="#">link</a>. Post-link text.',
+		    'This is <blockquote>foo</blockquote> < that.',
+		    'This is <blockquote>foo < bar</blockquote> that.',
+		    '< blockquote > < foo < blockquote >',
+		    'This is <blockquote>foo < < < bar</blockquote> that.',
+		    '<<blockquote>foo<</blockquote><',
+		    '<p>I <3 WordPress',
+		    '<3<div>foo',
+		);
+		$expected = array(
+		    'This is &lt; That. <blockquote>foo</blockquote> Text <a href="#">link</a>. Post-link text.',
+		    'This is <blockquote>foo</blockquote> &lt; that.',
+		    'This is <blockquote>foo &lt; bar</blockquote> that.',
+		    '&lt; blockquote > &lt; foo &lt; blockquote >',
+		    'This is <blockquote>foo &lt; &lt; &lt; bar</blockquote> that.',
+		    '&lt;<blockquote>foo&lt;</blockquote>&lt;',
+		    '<p>I &lt;3 WordPress</p>',
+		    '&lt;3<div>foo</div>',
+		);
+
+		foreach ( $inputs as $key => $input ) {
+			$this->assertEquals( $expected[$key], balanceTags( $inputs[$key], true ) );
+		}
+	}
 }