Dragging masked content outside the window

The clips window in Psycho studio contains the thirty-one clips that can be used by the site visitor to build a version of the shower scene. Obviously not all of the clips will fit inside the window, so I used a thumb wheel to drag this strip of thumbnail clips left and right. A mask is used to hide any content outside of the clip window, (the clips that are to the left or right of the display area). But this causes a problem. Because we have used a mask on the thumbnails, when we try to drag any of the thumbnails outside of the clip window, the thumbnails stay constrained inside the window! Fortunately there is a solution.