Unfortunately, running the URSim under VirtualBox has this glitch problem.
Althought I personally prefer use VirtualBox, in this case the best option for me is use VMware Player.
I actually had issues with VMware Player when installing the URSim, that is why I went to use VirtualBox. When using VMware Player, after I downloaded the URSim off UR download webpage, I could never find it in downloads when I searched using my VM. I contacted UR support and they advised to use VirtualBox.
It`s like a catch 22