webdriverio: Unable to simulate Select+All only under OS X

I have tried to simulate Select+All under OS X but without success. Everything works fine under Windows.

The code below works under Windows but not under Mac. The text never gets selected.

var CTRL_CMD = process.platform == 'darwin' ? 'Command' : 'Control';

it('test', function () {
  client.keys('some text');
  client.keys(CTRL_CMD); // the value here is correct
  client.keys('a'); // also tried with uppercase A
  client.keys(CTRL_CMD);
});

Update: I also tried using Meta and \uE03D