Just what the title says, the little rectangular Show Desktop button on the superbar causes the second bar to hide like it's a normal application.

Just as a note I tried to replicate this issue several different ways (using Windows 7 x64 Ultimate) and the taskbar has always stayed forefront for me

It says no full screen applications running, but it's happening now.

--- Machine ------------
Operating System: Microsoft Windows NT 6.1.7600.0
Operating System Version: 6.1.7600.0
Detected Version: Windows7
CPU: x64
Date/Time (UTC): 09/17/2009 04:57:52
Date/Time (Local): 09/17/2009 00:57:52
.NET Framework: 2.0.50727.4927
CurrentCulture: English (United States) (en-US ~ en)
CurrentUICulture: English (United States) (en-US ~ en)

--- Wallpaper ------------
Wallpaper Span: False
Monitor #1 Image: C:\Users\Mike\Pictures\Wallpapers\01974_cypresslookout_1680x1050.jpg (Exists: True)
Monitor #2 Image: C:\Users\Mike\Pictures\Wallpapers\01838_motionsenses_1680x1050.jpg (Exists: True)
Windows Wallpaper: C:\Users\Mike\AppData\Roaming\DisplayFusion\Wallpaper_2.jpg (Exists: True)
Generated Wallpaper Folder: C:\Users\Mike\AppData\Roaming\DisplayFusion

--- DisplayFusion ------------
Name: DisplayFusion Pro v3.1.3
Build Date: Sep 16, 2009 10:28
Pro: True
Pro License: ...5EIN-AE6A-JTlsbGi...
Command Line: "C:\Program Files (x86)\DisplayFusion\DisplayFusion.exe"
Current Folder: C:\Program Files (x86)\DisplayFusion
Performance Mode: False
Mouse Hooks: True
Application Hooks: True
System Hooks Pause FullScreen: False
Process Integrity Level: High
Font Scaling: 1

--- DisplayFusion x86 Hook DLL ------------
Path: C:\Program Files (x86)\DisplayFusion\DisplayFusionHookx86.dll
Name: DisplayFusion Hook
Prod Version: 1, 9, 0, 0
File Version: 1, 9, 0, 0
Size: 48,304 bytes

--- DisplayFusion x64 Hook DLL ------------
Path: C:\Program Files (x86)\DisplayFusion\DisplayFusionHookx64.dll
Name: DisplayFusion Hook
Prod Version: 1, 9, 0, 0
File Version: 1, 9, 0, 0
Size: 60,080 bytes

--- DisplayFusion x86 Hook Exe ------------
Path: C:\Program Files (x86)\DisplayFusion\DisplayFusionHookx86.exe
Name: DisplayFusion Hook x86
Prod Version: 1, 4, 0, 0
File Version: 1, 4, 0, 0
Size: 92,848 bytes

--- Monitor 1 (Primary:True ~ Real:True) ------------
Name: \\.\DISPLAY1
Bounds: {X=0,Y=0,Width=1680,Height=1050}
WorkArea: {X=0,Y=0,Width=1680,Height=1010}

--- Monitor 2 (Primary:False ~ Real:True) ------------
Name: \\.\DISPLAY2
Bounds: {X=1680,Y=26,Width=1280,Height=1024}
WorkArea: {X=1680,Y=26,Width=1280,Height=984}

--- Screens ------------
Count: 2
Point Min X: 0
Point Min Y: 0
Point Max X: 2960
Point Max Y: 1050
Total Width: 2960
Total Height: 1050
ActiveDesktop: False

--- Screen 1------------
ScreenID: 0
Device: \\.\DISPLAY1
Bounds: {X=0,Y=0,Width=1680,Height=1050}
MoveH: 0
MoveV: 0

--- Screen 2------------
ScreenID: 1
Device: \\.\DISPLAY2
Bounds: {X=1680,Y=26,Width=1280,Height=1024}
MoveH: 0
MoveV: 0

--- Managed Threads ------------
Count: 3
ID:3 ~ Name:TaskbarManager ~ Age:00:06:12.2892937 ~ Alive:True ~ BG:True ~ State:Background ~ Thread Name:TaskbarManager_07f624db-4a7b-4cff-a7a4-66c701e011d1
ID:4 ~ Name:HookManager ~ Age:00:06:12.2832934 ~ Alive:True ~ BG:True ~ State:Background ~ Thread Name:HookManager_5bac708a-d8d2-45db-b339-ab0f0aaab71b
ID:6 ~ Name:HookManagerProcess ~ Age:00:06:12.1902881 ~ Alive:True ~ BG:True ~ State:Background ~ Thread Name:HookManagerProcess_3321b940-9f78-4b15-8d84-db228814d26a

--- FullScreen Applications ------------
None

--- Taskbars ------------
Enabled: True
Auto-hide: False
Visual Styles: True
Visual Styles Detected: True
DWM Composition Detected: True
Opacity: 100
Flash Blink: False
Window Options: WindowsShowsAll
Button Width Max: 160
Button Icon Size: 32
Sizing Bar Size: 0
Count: 1

--- Taskbar 1------------
Location: {X=1680,Y=1010,Width=1280,Height=40}
Monitor ID: 2
Position (Setting/Current): Bottom / Bottom
TopMost: True
Buttons (2):
"Fringe - 116 - Unleashed.avi [16/20] - GOM Player" (021b15b8:021b15b8:021b15b8 ~ GCL_HIcon ~ None ~ {X=2348,Y=546,Width=650,Height=449})
"DisplayFusion Pro ~ Settings" (00220d1a:00220d1a:00220d1a ~ Icon_Big ~ None ~ {X=1944,Y=267,Width=751,Height=501})

--- Deleted Items (0)------------
None

--- Taskbar Items ------------
"Fringe - 116 - Unleashed.avi [16/20] - GOM Player" (021b15b8:021b15b8:021b15b8 ~ None ~ {X=2348,Y=546,Width=650,Height=449})
"DisplayFusion Pro ~ Settings" (00220d1a:00220d1a:00220d1a ~ None ~ {X=1944,Y=267,Width=751,Height=501})
"Show Desktop button in Windows 7 hides the DisplayFusion taskbar. - Mozilla Firefox" (00180c50:00180c50:00180c50 ~ None ~ {X=610,Y=23,Width=942,Height=893})
"µTorrent 1.8.4" (005a108a:005a108a:005a108a ~ None ~ {X=188,Y=79,Width=1285,Height=736})
"Sticky Notes" (00220f82:00220f82:00220f82 ~ None ~ {X=0,Y=0,Width=1,Height=1})

--- TitleBar Buttons ------------
Enabled: False
DisplayFusion Caption Button Size: {Width=35, Height=21}
System Caption Button Size: {Width=35, Height=21}

I'm talking about mousing over. Sorry, I guess I was kind of vague. There is code to make aeropeek ignore an application. Just saw something posted about it here http://www.neowin.net/forum/index.php?showtopic=794078 .