Node.js sync file permissions not working

.gitignore

*.txt

test.js

/* 
 * My system is Ubuntu Linux, so this is not Windows issue. 
 * My Node.js is v0.10.35.
 * Async calls seems to work OK, this problem seems to exist only on synchronous calls.
 */

var fs = require('fs');

fs.writeFileSync("test.txt", "Hello World", {
    encoding:"utf8",
    mode:parseInt("0644",8)
});

var f = fs.statSync("test.txt");

// Should be 33188 (100644) but is 33152 (100600)
console.log(f.mode);
console.log(f.mode.toString(8));

test2.js

/* 
 * Modes as string are not working either.
 * 
 * ------------------
 * 
 * My system is Ubuntu Linux, so this is not Windows issue. 
 * My Node.js is v0.10.35.
 * Async calls seems to work OK, this problem seems to exist only on synchronous calls.
 */

var fs = require('fs');

fs.writeFileSync("test.txt", "Hello World", {
    encoding:"utf8",
    mode:"0644"
});

var f = fs.statSync("test.txt");

// Should be 33188 (100644) but is 33152 (100600)
console.log(f.mode);
console.log(f.mode.toString(8));