Custom Cursor Blink Bug

Hi there!
I was playing my game when I found a very strange bug with the cursor. I have set a custom cursor and a fullscreen option (if you press "F" the game sets to fullscreen if it is on windowed mode and vice-versa). Also, I have set an auto-pause function that pauses the game when it's unfocused or when you press "P". My game window aspect is 4:3 and I have a 16:9 monitor, so when I turn fullscreen mode, there are black lines sideways to fill the screen, keeping the aspect ratio of the game. when I press "P" it pauses and if I press enter to continue with the game, this is what happens when the cursor is on those black lines:
Click to watch gif
Some Info:
OS: Windows 7 x64
GM: Game Maker Studio 1.4.9999 Professional Edition
Here is some screenshots of the game config:
I dont know what to do. If you could help me I'll be very grateful.