If I use this filter in Wireshark:
http.request.method == "POST" and use the vote buttons to vote for a stack exchange question, then Wireshark captures the corresponding POST request. I can also see in Chromes debugger that the request is a POST.
However, on another site that I'm trying to examine, when I click on a form button that triggers a POST (and Chromes debugger confirms that it is a POST) then Wireshark captures nothing.
Why might this be?
Thanks for all the tips. Utimately, I did get to examine a POST sent from my webserver using Fiddler, and it did help me out. I didn't mention it, but my webserver is Jetty running locally on Ubuntu, and I'm using Apache HttpClient for handling requests. For Java, if your not using HttpClient, this question is helpful. If you are, then check this question out.
In either case, Fiddler still needs to be setup to monitor HTTPS connections by checking the option at Tools --> Fiddler Options --> HTTPS --> Capture HTTPS CONNECTs