Description:
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After upgrading from 5.5.22 to 5.6.6 the script failed to operate correctly, churning out "Notice: undefined variable" errors on the function call line.

Disabling opcache fixes the problem.

Sadly the short version I've posted here doesn't appear to exhibit the problem, and I don't have time to anonymise the much larger section of code that's been breaking.

Nevertheless, it was 100% the call to "myFunction" that was giving a Notice undefined variable error.

Test script:
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$i=1;
${"sR{$i}S1"} = 'hello';
${"nR{$i}S1P"} = 'world';

myFunction(${"sR{$i}S1"}, ${"nR{$i}S1P"});

function myFunction($x, $y) {
    echo "$x $y";
}

Expected result:
----------------
echos

"hello world"

Actual result:
--------------
Notice: undefined variable