There is a bar below the caption track that separates it from the video track. Please make it possible to pull this bar downwards to reveal more of the caption track, in the same way that the bar separating the video and audio tracks can be moved up and down.
Currently, you can increase the caption track height by Option or Alt + mouse scroll. However, increasing the caption height this way only causes the upper portion of the track and its tools to disappear because the bar beneath the caption track is fixed. This makes no sense. This issue could also be deemed a bug, but I am putting it in as a feature request.