UNABLE to Resize Minecraft window

I've searched it but I only found errors occurring whenever you RESIZE your Minecraft window. This time, as you can see in the attachment below, I am in windowed mode (not fullscreen) and unable to resize the Minecraft window (the "maximize" button is unavailable; I am sorry I can't show it more clear with my cursor, the screenshot function does not recognise it)

EDIT: It only happens when you use F11 to toggle fullscreen!!!