No mate, that's normal. It's only a problem if aero doesn't turn back on.

Your computer may be low on memory or the game isn't compatible with Aero, so Aero is turned off until the game closes.

Originally Posted by MinecraftHD3

Originally Posted by Zaiden

At the moment I'm using Windows XP Professional x64 but I've been kinda wanting to switch back to Vista. One of the problems I had with Vista is that when I ran a few games (Mostly Call of Duty 4 and World at War) in windowed mode in the multiplayer part, Aero would turn off until I closed the game. Is there a way to fix this?

Here are my current System Specs:

AMD Athlon 64 X2 Dual Core Processor 5600+
4GB Ram
Nvidia Geforce 8800GTS 312MB

That means Desktop Window Manager is off. Turn it back on using the Troubleshooter.

Originally Posted by windude99

Your computer may be low on memory or the game isn't compatible with Aero, so Aero is turned off until the game closes.

This thread is coming up to 3 years old now, so I hope the problem has since been resolved!