Can't pin MP3tag window towards sides

Hi, everyone. For some reason, MP3tag 2.55a won't let me pin the application main window towards the sides. I'll explain: since Windows 7, if you click and drag a window title bar and move it toward either sides, the window will be maximized vertically, but horizontally it will occupy half of the display room, so you can have two windows side by side occupying each half of the screen.

It's the same as holding the windows symbol key and pressing the arrows: left or right, and up and down to maximize and minimize, respectively. When I try to pin MP3tag window in either sides, it doesn't pin, just moves and keeps the size. How can I fix it? I've attached a picture to illustrate the issue:

Im' running Windows 8 Core x64

Thanks in advance.