Cache problem?

[gvim]

I'm running a Perl/PSGI CGI::Application app on nginx via proxy_pass to Starman. The app logs form fields to a database and retrieves a resultset which is served up via Template Toolkit. Running on Apache as a plain vanilla CGI without the PSGI layer I can submit the form, press the Back button when the resultset is returned and re-hit the submit button, all within a second or 2 without any errors. However, with nginx + Starman the same app produces a random number of successful responses then returns an error page from the app as if there were 1 form field too many. It looks like some kind of cached response because even if I remove the module which runs this part of the app I still see the same app-generated error page. Since both nginx and Starman are returning a HTTP body there are no errors in the logs of either daemon to work with.

gvim