The issue may occur if the server sends a Cache-control:no-store header or sends a Cache-control:no-cache header. The WebGate provides configuration parameters to control setting these headers.
Following are the parameters and their default value:
CachePragmaHeader no-cache
CacheControlHeader no-cache
You can modify the WebGate configuration not to set these headers at all (the values for these parameters would be kept blank). By this, it would mean that Access Manager will not control the caching behavior.