On Windows 10, Windows Explorer will handle WM_SETTINGCHANGE notifications that are generated as a result of changes to a monitor's work area by recalculating the work area for all monitors attached to the system. This recalculation takes into account the size and position of the taskbar window on the monitor and any appbars on the monitor that are registered by applications calling the SHAppBarMessage function. It does not take into account changes to the work area that is made by applications calling the SystemParametersInfo function. This behavior is by design.
Windows Explorer's recalculation of the work area may override changes that an application makes to a monitor's work area while Windows Explorer is running. Applications that rely upon modifying the work area may not perform correctly on Windows 10.
Note This issue does not occur prior to Windows 10.