False negative: unused variable which has been changed

[jrfnl]

function foo() {
	$var = 'abc';
	$var = 'def';
	
	$var2  = 'def';
	$var2 .= 'ghi';
	
	$var3  = 10;
	$var3 += 20;
}

For the above code, I would expect three errors for unused variables, one each for $var, $var2 and $var3, but only $var is reported as unused.

Looks like this is related to the use of combined assignment operators.

[jrfnl]

FYI: I have a fix ready for this, but need a decision on #108 before I can pull it.