Comments “load more” duplication

We have a number of WordPress instances using wpDiscuz to handle commenting. We are hosted with WordPress VIP (Automattic’s enterprise hosting service).

We are noticing that the “Load more” button is not working correctly. It works correctly the first time you click this, but re-loads the same batch of comments on all subsequent “load more” clicks.

I can see that the admin-ajax load is sending the correct requests, however I believe it is receiving a cached response each time.

I appreciate that this may be a VIP-specific issue (although they point at the code), but any suggestions would be greatly appreciated.