Media Encoder CC 2018 cannot change export format/preset

Steps to reproduce (on Os X El Capitan)

1) Open Media Encoder CC 2018

2) Drag a video file (e.g. .mp4)

3) click on the codec or preset link of the file

4) after window opens, click on the "format" or "preset" drop-downs, under export settings.

Outcome:

The window would lose focus, no drop-down menu appears.

EDIT: I upgrade to OS X High Sierra and the feature works as expected.

So it's a bug on El Capitan and possibly Sierra