Pinterest has since released a Javascript which provides a button to pin images. I’ve switched to that and it works fine.
@asaturn: your solution seems like the likely answer to my problem.
@mrsztuczkens: sorry for not responding earlier, the previous reply notification must have gotten lost in my inbox.
You can either do it from your APC admin page (apc.php), if that’s accessible to you, or in the W3TC Dashboard.
The W3TC Dashboard has two buttons saying Empty APC Cache and Empty OPCode Cache at the top. Press those and you should be fine. If you don’t have W3TC installed, perhaps you can find cache clearing buttons in the dashboard of your caching plugin.
Nevermind, resolved after emptying APC cache.
