I'm running a fresh install of Dapper with screensaver set to 'blank screen', and 'lock screen when screensaver is active' enabled....
If a panel menu (e.g. Applications) is open and the machine is left idle, the screen fails to lock. It fades out after the time period as expected, but the desktop reappears after a few seconds.
It's an inherent issue with the X11 (X.org) design. It has been looked into by a few big developers but solving it is lose to imposible. The solution will be switching to Wayland instead of X.org, somthing that likly will happen in the not to fare away future.
(il semble que le bug ait été finalement corrigé, je ne sais pas trop comment... 8 ans plus tard
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