Orchestration remains in active state when it should dehydrate

Hi,

We are trying to implement following scenario in BTS:

1, the application should receive a InMessage from a one way file folder

2, after receiving InMessage, application would wait a UIRequest. In this step, UIRequest with the same correation ID always comes after InMessage, but can not sure the exact arriving time.

3, UIRequest should be submitted by a request and response SOAP port

4, Application must utilize information from both InMessage and UIRequest to generate the acknowledge of UIRequest 

 In order to achive this functionality, we have implemented two orchestration as follows:

Orchestrations Main.odx and UIInteraction.odx. Main.odx receives a input message from a FILE Folder, initialises a correlation and invokes second orchestration UIInteraction.odx using Start Shape. Main orch passes the input message and a initialised correlation to UIIntegration orchestration. The UIInteraction orch waits for a request from UI based application through a web service (request-response) port and sends a response back to UI. The response also include message details passed by Main orch 

When I run this implentation in BizTalk, it works for the first time. but on the second message UIIntegration orch does not dehydrate and remains active, due to which web service call from UI fails, because UI request does not correlate to any waiting orchestration instance. If I restart the BizTalk host instance then UIIntegration orch instance dehydrates immediately and it starts working correctly. However If we keep waiting for the orchestration to dehydrate then it takes around an hour to dehydrate.

Can you please suggest any solution to the problem.