Screen not locked when coming out of suspend/hibernate

Occasionally, after coming out of suspend the screen sometimes is unlocked and visible for over a second before the lock screen kicks in. I'm pretty sure I've managed to click on stuff when the lock screen has been particularly slow to kick in.

The screen also shows a message box saying "Computer will suspend very soon because of inactivity" - which needs OK/Cancel clicking as it doesn't go away on its own after waking. Not sure if this is related as it happens even if the problem itself does not occur. Thought I'd mention is for completeness but I think it's already been reported as a bug in its own right.

My computer is configured to do nothing on screen close (it does lock when the screen turns off, which happens on lid close), but to suspend only after 5 minutes of inactivity. This appears to work correctly every time. I can finish using it, close the lid then it suspends 5 minutes or so later.

I'm partly inclined to consider this a security vulnerability, but mainly find it a little frustrating and confusing.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: gnome-screensaver 3.6.1-0ubuntu7
ProcVersionSignature: Ubuntu 3.11.0-17.30-generic 3.11.10.3
Uname: Linux 3.11.0-17-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.2
Architecture: amd64
Date: Thu Jan 30 19:58:28 2014
EcryptfsInUse: Yes
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session idle-delay uint32 300
 org.gnome.desktop.session session-name 'ubuntu'
InstallationDate: Installed on 2013-05-07 (268 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screensaver
Symptom: security
Title: Screen not locked when coming out of suspend/hibernate
UpgradeStatus: Upgraded to saucy on 2013-12-02 (58 days ago)