I took the time to check this behavior on 6 different machines that I have access to. All of them display the same change. When not maximized there is a fixed-pixel-width border on all four sides of the screen. When the program is maximized that border disappears. The cursor in the search window is a certain distance from that border in the non-maximized state. When the program is maximized it seems that the cursor is then that same distance from the left edge of the now borderless screen. So at least it seems that there is no actual loss of information when the program is maximized.
It appears that I found a bug in the program in the process of checking this out.
Go to Main toolbar, Tools, Options, General, Flags, Startup Options, System Scaling Options.All of the machines were set to the first option. I reset the option to the second, followed the instructions to close and restart BW. But after that the choice always reverted to the first option. I added a reboot, ran with admin privileges, and on different Windows OS's, but could not change the setting.