1776 still have the same issue sometimes.
and I found sometimes when switching screens, all icons on some desktops would be hidden and right click mouse on desktop can not popup the menu(I didn't enable anything in "Desktop elements" tab).

Are you sure this is with build 1776? There already is a fix for a problem with the same symptoms in that version.

Same issue what I met.

I am using:
Dexpot Version 1.5.99, Build 1776
Windows 7 Home Premium, 64 bit: Version 6.1 (Build 7601: Service Pack 1)
I am using the classic windows theme with almost all visual effects disabled.

Problem: When switching between screens quickly sometimes windows will be copied to multiple desktops.

I am using DexGrid (3 x 3) to switch desktops.
I have
[Windows]+[Alt]+[Arrow key] hot key assigned to switch desktops
[Windows]+[Ctrl]+[Arrow key] hot key assigned to move windows
[Windows]+[Tab] hot key assigned to full screen preview.
All other hot keys are disabled. In particular, I am not accidentally hitting the one to copy windows.

Steps to reproduce error:
Open up a few windows, I noticed it with a 2 instances of Chrome and Explorer. Not too many though, or the lag stops the error from happening (apparently).
Rapidly switch back and forth between windows (using hot keys described above).

Running applications:
Dexpot
Chrome
Explorer

This *sounds* like a problem resulting from multiple threads running at the same time competing with each other.