This behavior is by design.

The PHP closing tag ?> generates an implicit ; (semicolon), and thus, terminates any statement.  For instance:

<?php print "foo" ?>

will work, because the closing tag will implicitly close the print statement.

In your case, when you use <? } ?> to close your IF block, you're also terminating the entire statement, and thus, you cannot use 'ELSE' afterwards:

if (...) {
   ...
}; else if {        // <-- invalid!
   ...
}