Bug OP test, result:

( ! ) Parse error: syntax error, unexpected ':' in /var/www/php_bugs/mixed_control_structure.php on line 5


PHP Version 5.2.10-2ubuntu6.4

System 	Linux 2.6.31-20-generic x86_64
Build Date 	Jan 6 2010 22:36:47
Server API 	Apache 2.0 Handler 
PHP API 	20041225
PHP Extension 	20060613
Zend Extension 	220060519
Debug Build 	no
Thread Safety 	disabled
Zend Memory Manager 	enabled 

Apache/2.2.12 (Ubuntu)

So, what's happening is that the parser is associating the else: with the normal 
style if block on the line immediately above it, and of course mixing in a 
single if/else like that is verboten.

Should it be fixed? Probably, but it's a serious edge case, and massaging the 
parser to cope with it is much harder than the following workaround:

<?
if(2>1):
	echo "ABCD";
	if(4>3){ echo "EFGH"; };
else:
	echo "123456";
endif;
?>

Note the extra semicolon added after the inner-if statement.  This is enough to 
terminate that expression and ensure that the else statement binds to the right 
if.

Leaving this bug report open, because it is definitely a bug, but I'm not sure 
who's going to invest the cycles on it.

Seems to be no bug for me, because documentation writes (at http://www.php.net/manual/en/control-structures.alternative-syntax.php):

Note:
Mixing syntaxes in the same control block is not supported.

This code causes no syntax too, because the if { ... } is in {...} control block:

<?php
if(2>1):
	echo "ABCD";
	{if(4>3){ echo "EFGH"; }}
else:
	echo "123456";
endif;
?>

Changing to not a bug as mixing syntaxes in the same control block is not supported.