Sorry, your prefs.prop files don't work with the installed demo version 126.96.36.199 on my system. After replacing the original prefs.prop the game starts in windowed mode. But after changing back to full screen mode it still uses the 1024x768 resolution instead of the 1280x1024. Your prefs.prop file is replaced with a new one (smaller size, only 784 byte).
I tried to start the demo without a prefs.prop file in the folder and the demo generates a new one with a size of 768 byte.