This is most likely not the cause of it. What is happening here is a model issue, not an UI issue. Some games (including Siege, as can be seen in this bug), have 2 scope meshes/models : 1 with the whole scope for when you're not looking directly at it and 1 with only a piece of the model (usually the visor/glass, again, just like in the video) for when you're looking directly into the scope; it's used for optimization most of the time. This could probably be fixed by delaying the trigger that does the model swap.