The pm-utils and its configuration is fine, and maybe so of the network-manager.
I am able to further decouple the problem -- If I boot into text mode console, I am able to do "close the lid then open & wake it up" many many times without interruptting my wired & wireless network, while under Xorg (with fluxbox as WM), if I close the lid then open & wake it up, my wired & wireless network will be gone. If I close the lid a second time, the machine won't even go to the suspend stage again.
Conclusion: I think the problem has something to do with Xorg.
The pm-utils and its configuration is fine, and maybe so of the network-manager.
I am able to further decouple the problem -- If I boot into text mode console, I am able to do "close the lid then open & wake it up" many many times without interruptting my wired & wireless network, while under Xorg (with fluxbox as WM), if I close the lid then open & wake it up, my wired & wireless network will be gone. If I close the lid a second time, the machine won't even go to the suspend stage again.
Conclusion: I think the problem has something to do with Xorg.