The up/down arrows don’t change the quantity of tickets in Events Calendar Pro. Instead, the browser view jumps to the top of the browser window when either the up or down arrow is clicked. Here’s an example:
http://www.mavenmakers.com/event/the-design-process-for-beginners-free-for-fast-pitch-participants/#
The arrows do work, however, once you click “Add to Cart” and are taken to the shopping cart.
I’ve searched through your knowledgebase, and the closest answer I could find is that there might be a problem with the theme (Dante), but I’ve been unable to find a solution. I thought maybe it was a z-index thing, but I can’t find any z-index settings in the stylesheets that seem to apply.
I’ve reverted to the Twenty Fourteen theme, and the arrows work fine. So I guess it’s a theme conflict after all.
I’m using Chrome on a Mac, and the problem is the same on Firefox and Safari on Mac as well.
Please let me know if there’s any more information I can provide.