Hotkey from MacBook to Mac VM via vSphere Web Client

Hi,

Some of our Mac customers have trouble on sending hotkey(Command+C and so on) from their MacBook to Mac VM running on ESXi5.5, yet it works for method from Windows to Mac VM via vSphere Web Client

Is there special setting we need care to make hotkey work from MacBook to Mac VM via vSphere Web Client5.5?

BTW, installing plug-in or not won't make it work.

thanks,

Robinson