Description:
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There probably should be an explicit reference to this:

"While not being strictly an assignment by reference, expressions created with the language construct array() can also behave as such by prefixing & to the array element to add.

The page also explains your why your first code behaves like it does:

    Note, however, that references inside arrays are potentially dangerous. Doing a normal (not by reference) assignment with a reference on the right side does not turn the left side into a reference, but references inside arrays are preserved in these normal assignments. This also applies to function calls where the array is passed by value." (taken from http://www.php.net/manual/en/language.references.whatdo.php)

at the documentation page for 'array':
http://php.net/manual/en/language.types.array.php

[coming from http://stackoverflow.com/questions/6072444/php-array-copy-semantics-what-it-does-when-members-are-references-and-where-is/]