Solved Windows has stopped "windowing"

I am trying to work with two windows opened, sharing the screen. One is a file in Word 2007, the other is a PDF file. Each taking half the available screen space, one above the other.

That's fine provided I am working in the last of those windows that I adjusted. As soon as I click on the other window, either within the window or on its icon in the taskbar, the window becomes full screen!

I have for a long time had the option "prevent windows from automatically being resized" set, with no problem, and it is still set.

Do you have any idea why this has suddenly started happening? This is very strange behavior, and as such Windows is not functioning at all as "windows," just "screens."

Some clues ...

I have my programs set up individually so they as "normal" but are full screen. That is, the "maximize" rather than the "normal" button is showing in the upper-right corner. I have run this way for a long time, to ensure that everything always opens maximized; then on the infrequent occasions that I need more than one window on the screen at a time, I resize them smaller. This had worked flawlessly until now, and I could make any window active without its size being maximized.

Now too, some pop-up boxes like the connection box when I am uploading an email message are also opening full-screen instead of as small boxes. This had never happened before.

Today, after the problem occurred, I did try this. I set both programs mentioned in my prior post to run "maximized" (they were already set to "normal") in a shortcut for each on my desktop, saved that and then changed them back to Normal. That did not fix it.

It seems it could be a Window Manager problem, but my testing suggests it isn't. I ran SFC /scannow, and that finished clean. I tried stopping and restarting Desktop Window Manager Session Manager, and even disabling it, but the problem still persisted no matter what.

Also, I am running on the Classic desktop theme, so no Aero.

I fixed it! I forgot that several weeks ago I tried a "maximize all windows" setting in TitleBarClock. Since I rarely need multiple windows on the screen at once, it was out of mind. And as I found today, it didn't work as expected.

The way I found the problem was by using msconfig.exe (from Start's run box) to disable half of my startup programs at a time, and finding and end to the problem then narrowing down the program causing it.

Thanks for posting your fix.