http://stackoverflow.com/questions/24...
so here I am searching for the solution for this weird problem! Seeing none of the other answers working for me, I did the random most thing I could think of and it worked.
Open SceneBuilder (a brand new one). Go to File Open Recent Clear Menu. Close Scene Builder.
Now the bug should be fixed (it did for me)
PS: I am ashamed of posting this answer. But since this is a nasty bug which wasted time, I don't want anyone else to waste theirs