I was playing in Minecraft in full screen for a while (toggling using F11) and then after a while, I went back to windowed mode (I don't like playing in full screen, I was just testing the functionality of it for... reasons).
However, when I went to maximize the window (not full-screen) I realized the maximize box in the corner had become disabled. I fiddled with full screen a bit more, toggling it in the menu options as well as toggling it with F11, but this had no effect. Restarting Minecraft (closing it completely and re-opening, not just quitting to menu) did fix it however.
Does anyone know what causes this issue, and if restarting Minecraft is the only way to fix it?