I am having the same problem.  If an attribute has an extra quote in it, will cut off all the text afterwards.  

Example Input:
----------------
strip_tags('
text before link
<a href="http://google.com"">google.com</a>
text after link
test 1
test 2
')


Expected Output:
-----------------
text before link
text after link
test 1
test 2


Actual Output:
--------------
text before link



Note, I do not have this problem in PHP 5.0.4 or previous versions

Thank you for taking the time to write to us, but this is not
a bug. Please double-check the documentation available at
http://www.php.net/manual/ and the instructions on how to report
a bug at http://bugs.php.net/how-to-report.php

The parser continues until it founds the end of the tag, which can not be in an attribute value (XML allows all characters except [%&'] in attribute values).

In the given examples the attribute value never terminates and the end of the tag is never found, which causes the rest of the string to be truncated.

This change as been made to fix the following bug: http://bugs.php.net/bug.php?id=40432

Character \ is allowed in tag attribute, so strip_tags('Hello <a href="any\"> World') leading to "Hello" (without "World") is bug.

PHP 5.x patch:
Index: ext/standard/string.c
===================================================================
--- ext/standard/string.c	(revision 284189)
+++ ext/standard/string.c	(working copy)
@@ -4367,7 +4367,7 @@
 					tp = ((tp-tbuf) >= PHP_TAG_BUF_SIZE ? tbuf: tp);
 					*(tp++) = c;
 				}
-				if (state && p != buf && *(p-1) != '\\' && (!in_q || *p == in_q)) {
+				if (state && p != buf && (state == 1 || *(p-1) != '\\') && (!in_q || *p == in_q)) {
 					if (in_q) {
 						in_q = 0;
 					} else {

Trunk patch:
Index: ext/standard/string.c
===================================================================
--- ext/standard/string.c	(revision 284189)
+++ ext/standard/string.c	(working copy)
@@ -6519,7 +6519,7 @@
 				tp = ((tp-tbuf) >= UBYTES(PHP_TAG_BUF_SIZE) ? tbuf: tp);
 				*(tp++) = ch;
 			}
-			if (state && prev1 != 0x5C /*'\\'*/ && (!in_q || ch == in_q)) {
+			if (state && (state ==1 || prev1 != 0x5C /*'\\'*/) && (!in_q || ch == in_q)) {
 				if (in_q) {
 					in_q = 0;
 				} else {
@@ -6763,7 +6763,7 @@
 					tp = ((tp-tbuf) >= PHP_TAG_BUF_SIZE ? tbuf: tp);
 					*(tp++) = c;
 				}
-				if (state && p != buf && *(p-1) != '\\' && (!in_q || *p == in_q)) {
+				if (state && p != buf && (state ==1 || *(p-1) != '\\') && (!in_q || *p == in_q)) {
 					if (in_q) {
 						in_q = 0;
 					} else {


Test case:
--TEST--
Bug #45599 (strip_tags() ignore backslash (\) character inside html tags)
--FILE--
<?php
echo strip_tags('Hello <a href="any\"> World') . "\n";
echo strip_tags('Hello <a href="any\\"> World') . "\n";
echo strip_tags('Hello <a href=\"any"> World');
?>
--EXPECT--
Hello  World
Hello  World
Hello  World

This bug has been fixed in SVN.

Snapshots of the sources are packaged every three hours; this change
will be in the next snapshot. You can grab the snapshot at
http://snaps.php.net/.
 
Thank you for the report, and for helping us make PHP better.