I used to run Fluxbox on Ubuntu as well as on Linux Mint (standard) 7 and 8, and I had this exact same problem then. I close my laptop lid and leave the laptop idle for several minutes.
When I open the lid again, I'm treated to a blank
screen (not the screen saver I have set in Xscreensaver), and when I try to work, I find that my screen has been locked. I should add that in Xscreensaver, the "Lock screen after X minutes" checkbox is unchecked
Also, under the "Advanced" tab in Xscreensaver, I have display power management disabled.My solution
to this problem before was to add "gnome-power-manager &" to my .fluxbox/startup file, which seemed to force things to behave.
However, since gnome-power-manager isn't installed in Linux Mint 8 Fluxbox CE (and I'd like to avoid installing it if at all possible), this isn't a solution.
In fact, I've been meaning to ask... since there's no gnome-power-manager, and there doesn't seem to be an equivalent anywhere that I can find that's present out of the box, what is the recommended way to manage my power settings in this release? I like to be able to control what happens when on AC, when on battery, when the lid is closed in either of those cases, et cetera.