Sites like Google and YouTube often take advantage of their huge user base. They roll in design changes and rely on the live test data from millions of users.
Recently, YouTube has been making lot of changes to its interface. It maintains 2 base UIs with regular updates to each. The 2 UIs keeps switching randomly. This is really irritating when a interaction is significantly different between the 2 UIs, like the volume bar. For one video you are moving the bar horizontally and for the next video you are moving it vertically.
Vertical Volume Bar:
Horizontal Volume Bar:
Aggravating the situation is the interaction in both these volume bars. The volume bar is visible only when you hover over the speaker icon. This is intuitive. But the problem arises when the user interacts with the volume bar. The target area is volume bar area plus speaker icon area. As soon as the cursor exits the target area, the volume bar is lost instantly. I have encountered this problem a lot. It is hard to restrict the cursor within the target area, especially when you are trying to reach the max volume, which is a very common scenario. This slows down the users and makes them repeat the action.
One of the ways to solve this problem is to have a small delay before the volume bar disappears. So even if the user misses the target, we would give them enough time to correct their action.
Umanka Karkada - UX Blog 