I currently run a dual-monitor setup at my desk-my laptop's built-in display and a somewhat large LED TV. The TV is set as the main monitor in Windows. When running Minecraft full-screen on my TV screen, it works perfectly fine... until I click off to a window on my laptop's screen, (notes, tutorials, stream chat, etc.) where the Minecraft window minimizes itself. I have to click on the crafting table icon in my taskbar to bring it back up.
Can confirm 1.17.1-rc2, 1.17.1