When using the Dreamcast mouse, the Windows OS cursor doesn't lock onto the DEMUL window hence its possible to drag the cursor off the window, press a mouse button and accidentally make Windows focus on whatever your cursor is hovering over. This is mostly an issue in Windowed mode, but does affect Full screen mode as well.
When fixed it would also be a good idea to make the Windows OS cursor invisible when locked onto the DEMUL window.
When using the Dreamcast mouse, the Windows OS cursor doesn't lock onto the DEMUL window hence its possible to drag the cursor off the window, press a mouse button and accidentally make Windows focus on whatever your cursor is hovering over. This is mostly an issue in Windowed mode, but does affect Full screen mode as well.
When fixed it would also be a good idea to make the Windows OS cursor invisible when locked onto the DEMUL window.