Dear i have been using this feature for sometime now, but this is the first time i am facing issues.
Dear? So you think that statement answers any of my questions above? How do you expect anyone to be able to help finding the problem if you can't provide any details and answer the questions we have?
I didn't ask all those questions to try telling you you have done anything wrong if that's what you thought, I asked them because knowing the answers would help pinpointing the problem and make it easier to reproduce the problem.
I've tried to reproduce the problem but cannot. I've tried 3.13, 3.17, 3.18, 3.20, 3.21(beta) and they all work perfect for me. They work both in transparent mode (redirecting 80 -> 8080) for HTTP, in normal proxy mode and with and without a parent proxy. I havn't been able to test fully without a parent proxy though as the network I'm testing on does not allow direct outbound connects, but I can see correct requests are sent out my external interface.
While testing I found bug though that causes the web-proxy to use the wrong src-address when processing requests that come from a client on the internal interface and the dest server is on the external interface. It then incorrectly picks the internal IP address as src-address when sending out the request to the dest server. So you might wanna test explicitly setting src-address to the IP address you want it to use.
This problem seemed to exist also in 3.13 and 3.17 as well as the newer ones so it shouldn't be your problem, unless something else changed at the same time causing you to get punished by this bug just at this time.