chunking causing latency in iRule?

I thought chunking on requests is quite rare, so that's strange. Usually POSTs tend to use multipart encoding, which is similar to but not the same as chunking, and in that case using HTTP 1.0 or 1.1 shouldn't make a difference. It's difficult to guess what's going on without seeing the packet captures. Is there by any chance a content-length used in HTTP 1.0 and not HTTP 1.1?