Sorry for the late answer, I've been a little busy these days.
So, accordingly to what you have described, it seems that you have some misconfiguration in your power management.
In some cases the suspend is managed by the gnome-power daemon, which takes all steps needed for a correct suspend cycle (one of them is to activate the screensaver) and at resume everything is ok, in other cases it's like the gnome-power daemon is not used and the suspend cycle fails.
Take a look at the 'gnome-power-manager' options and check they are all correct, also look at its advanced options by using the 'gconf-editor' utility (options are in /apps/gnome-power-manager).
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