Some simple test cases. Perl v5.8.8 on Linux and WinXP acted the same.

my @testsubs;

## test 1
push @testsubs, sub {
    return do {
        1;
        1;
    }
};
 
## test 2
push @testsubs, sub {
    if (1) {
        return do {
            1;
        }
    }
};

## test 3
push @testsubs, sub {
    if (1) {
        return do {
            1;
            1;
        }
    }
};

## test 4
push @testsubs, sub {
    if (1) {
        return scalar do {
            1;
            1;
        }
    }
};


for (1..@testsubs) {
    print "test $_ ", 
        $testsubs[$_-1]->()==1 ? 'passes' : 'fails', 
        "\n";
}
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Output:

test 1 passes
test 2 passes
test 3 fails
test 4 passes
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