Computer Type PC/Desktop System Manufacturer/Model Number MSI MS7360 OS Windows 10 Pro x86 and x64 dual boot CPU E8400 Core 2 Duo Motherboard MS 7360 P35 V1.0 Memory 4GB Aenon DDR2 667 Graphics Card Asus Geforce GT610 Sound Card Realtek HD Audio AC888 Monitor(s) Displays Dell Sharpscreen 22 inch Screen Resolution 1920x1080
Keyboard Logitech G11 Mouse MS Comfort 4500 PSU Corsair 500W Case Thermaltake Case Cooling CPU Artic Freezer Hard Drives Hitachi 500gb Backup
Seagate 500gb Data drive
Crucial SSD 500gb MX200 SSD Boot Internet Speed 17mbps Browser Firefox Antivirus MS Defender
More than likely it's just a fallback. The problem here is that you're "locking" the menu mode on in a roundabout way, and the DWM rendering is unable to render the new alt-tab functionality in that mode, so Windows falls back to non-DWM alt-tab functionality. You would get the same if you disabled theming.
It's not an easter egg, it's more of a side-effect of the modal locking done by the menu system, combined with DWM rendering. In effect, it's a "hole" in the DWM renderer.
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