The upper one is Safari and the lower one is Orion RC.
When a window is partially offscreen and a user drags a tab out of it, the preview window gets cropped.
The animation is also not as seamless as Safari's due to the brief disappearance of the preview window when releasing it.
Version 0.99.128.1.1.2-rc (WebKit 619.1.11.111.2)
Sonoma (14)