In the current setup of ubuntu budgie, triggering the expose view with a hot corner, while a view is already open will just create another instance of the expose view, instead of closing the current instance, which i think would be the more intuitive behavior. Its how most other DEs (like cinnamon or pantheon) do this.
This was fixed quite a while ago. What is your UB version? Are you fully updated? We chose however not to toggle, but simply do nothing if the corner is hit again. Press escape, pick any window (either clicking or pressing) or click next to the previews to close. As said, you must be using quite an old version if an additional previews appears.
oh wait, its fixed now. Just realized. Thank you!