AppHarbor - Why is my <httpRuntime maxRequestQueryStringLength=“XXXX”/> not working?

Question

I have a long querystring value I need to pass in (itself a questionable practice, I understand), and I am not able to get it to take effect on my Appharbor app instance.

Locally, I've made this change to my web.config and confirmed that the URL in question works locally:

<httpRuntime maxQueryStringLength="2097151"/>

And ensured that it exists in the resultant web.config post the transformation by my Web.Release.config. That said, when I push to AppHarbor, the transformation should pick it up...yet I'm still getting this exception:

The length of the query string for this request exceeds the configured maxQueryStringLength value.

Stack Trace:

at System.Web.HttpRequest.ValidateInputIfRequiredByConfig()
at System.Web.HttpApplication.PipelineStepManager.ValidateHelper(HttpContext context)

Any ideas? Thanks for your help.