Menu shadows error

[gacondilonton]

When i click to menu, left of spread menu have shadows similar below image

http://vinagroupviet.com.vn/images/Menu_002.pnghttp://oceanlaw.vn/images/Menu_002.png

But when i click it again, shadows does not appear

http://vinagroupviet.com.vn/images/Menu_001.pnghttp://oceanlaw.vn/images/Menu_001.png

Other menus also have this problem
Please tell me way to shadows always appear
Thanks