I'm not sure of the real answer. The link below is to a tutorial about using strings. It refers to simple and complex variables and says:
http://www.zend.com/zend/tut/using-strings.php
"Referring to complex variable combinations inside strings may not produce the expected results".
Great! It is best to take the "may not" out of the equation and just make sure it works.
So you do stuff like:
echo "My array value is: " . MyArray[$i];