Apps Tablet Multi Pane - Left Pane is SHADOWED

[decken]

Hi, Everyone,

I modified below codes to let my tablet show multi panes in Settings:
1. packages/apps/Settings/src/com/android/settings/Settings.java
@Override
public boolean onIsMultiPane() {
//return false;
return true;
}
2. frameworks/base/core/res/res/values/bools.xml
<bool name="preferences_prefer_dual_pane">true</bool>

But, the LEFT PANE's right half is SHADOWED by something.
Although I traced codes in packages/apps/Settings/src/com/android/settings/Settings.java and searched all the codebase to find some clues, I still cannot get it right.

I attached the picture for your information.
Thanks for your help.

https://www.dropbox.com/s/zwagl4eiiwd550a/multi%20pane_left%20pane_SHADOWED.png?dl=0

Cheers,
Decken