npm ls "forgets" nested linked dependencies when run programmatically

[cressie176]

npm.commands.ls drops nested linked libraries when run programmatically. e.g.

module-a/package.json

{
    "name": "module-a",
    "dependencies": {
        "module-b" : "*",
    }
}

module-b/package.json

{
    "name": "module-b",
    "dependencies": {
        "module-c" : "*",
    }
}

module-c/package.json

{
    "name": "module-c",
}

npm.load({}, function() {
    npm.prefix = './work/module-a/';
    npm.commands.ls(undefined, true, function(err, full, lite) {
        console.log("Module A\n", lite);
        npm.prefix = './work/module-b'/;
        npm.commands.ls(undefined, true, function(err, full, lite) {
            console.log("Module B\n", lite);           
        });
    });
});

The output from the second 'ls' command does not list Module C as a dependency of Module B

The bug is in read_installed, and to do with the use of rpSeen. While traversing module-A's dependencies npm correctly detects that Module-B depends on Module-C, but after returning, this information is not present in the object stashed in rpSeen.