Hi Nick, the behavior is a bug with some instances of Chrome. We're looking into it but it's been difficult to troubleshoot - it's only happened a handful of times. Haven't figured out yet what specifically is causing the issue on some machines. The behavior can vary even between machines with comparable specs / graphics cards, etc.
We'll figure it out but in the interim, unfortunately, the workaround is to use a different browser when sharing (or use item details page, if that is appropriate for the worklow). One thing you could also try is to uninstall / reinstall Chrome (I believe settings, bookmarks, etc will persist). Haven't had the opportunity to try this when we've had a repro case, but it may work..
Thanks,
Chris