I have install MacBuntu-OS theme and I found the shadow issue is gone(restart application). So it should be a elementary-theme issue not Gala. I have attached two image, one with elementary theme and other with MacBuntu-OS theme.
MacBuntu-OS theme: https://s6.postimg.org/xrnj9h21t/Screenshot_from_2016_08_10_13_22_17.png
Elementary theme: https://s6.postimg.org/5q9hvrwrl/Screenshot_from_2016_08_11_00_15_41.png
I have install MacBuntu-OS theme and I found the shadow issue is gone(restart application). So it should be a elementary-theme issue not Gala. I have attached two image, one with elementary theme and other with MacBuntu-OS theme.
MacBuntu-OS theme: /s6.postimg. org/xrnj9h21t/ Screenshot_ from_2016_ 08_10_13_ 22_17.png
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Elementary theme: /s6.postimg. org/5q9hvrwrl/ Screenshot_ from_2016_ 08_11_00_ 15_41.png
https:/