Your cursor is likely getting stuck on your main monitor due to having a higher res. Think of it like a big box and a small box connected, the two monitors are connected through a tunnel, in which the tunnel is as large as 1280x1024. If you try to move your cursor where you're still in a 1080p zone, it won't move over to the 1280x1024 monitor. Same thing happen with my 1440 and 1080p monitors. Hope that made sense.