Windowed mode problem

[Brain]

So I always play in windowed mode (basically full screen, just windowed) so that I can alt tab better, etc...

However, every now and then EQ won't let me alt tab and cycle through my devices, as it "overrides" everything. In other words, the only way I can look at my internet page while playing EQ is by minimizing the window whereas I used to be able to just alt tab back and forth.

Anyone know what causes this problem and/or how I can fix it?

Thanks