Windows 7's desktop window manager has a lot of nifty features with respect to how it interprets your window movements. Based on that it automatically places, resizes, minimizes and maximizes windows and that may be what you were seeing.
Don't have a complete list (or a handy link) of the features, but here are a few things to try:
1. Grab a window (that does not occupy the entire desktop) by the toolbar and take it to the top of the screen and release - it will maximize
2. Grab a window & move it to the left (right) edge of your display - Win7 will show you that it would occupy half the screen if you released.
Windows also recognizes "shake" gestures to return window to their original sizes. I believe there's a web page/video on MS's Windows 7 web site that goes through these new shortcuts.
Himanshu Gohel
Autodesk, Inc.