OK, I resolved the problem. The client is using Cloudflare and had Rocket Loader switched on. Switching off Rocket Loader fixed the issue.
Well, that works, except that simply moves all the images to the left – how did you then get the images back to being centered with the appropriate spacing between?
I am also having this problem. A little bit disturbed to see no other responses for 6 months! Did either of you manage to resolve this little problem?
I am also having this problem. Happens in both Chrome and Safari on OS X. If I mouseover the thumbnail that is misplaced and it jumps back to the correct spot.
Also using 2.2.4
