Gerard, I had this same issue and resolved it setting the screen to full screen.
BUT, I am facing a similar situaton, as I posted here Bug when using grouping in a horizontal Inline List?
When I use horizontal in-line list without grouping it is normal. But when I choose a grouping by category occurs something strange:
I slide the top one category (or the second one) and what in fact slides is the botton one. 
I did a video, but I don´t know how to upload it here in the forum.