I am not able to reproduce, it is working on my Mac system using Safari Chrome and Fire Fox.
In the additions gallery, the 3 story with snow on the ground was at position 1, I have been able to move it to position 4 in Safari and other positions using other browsers on Mac.
must be a specific browser setting or plugin on your clients machine that is causing the problem. you might want to try resetting the browser to its default settings and disabling any browser add ons.
http://www.howtogeek.com/171924/how-to-reset-your-web-browser-to-its-default-settings/