I'm testing a 32-bits ISAPI extension on a web-server with IIS 7.5 and get strange behaviour in some cases. At a certain point in the web application, a URL serves a large (a few MB) JPEG file directly to the client (Content-type: image/jpeg).
The image gets transmitted for a first part, but the response seems to halt for an unknown reason. Nothing happens until, from another browser, another request comes in and gets handled. Then another few KB of the image gets sent to the client. Only if I fire a couple of small requests from the other browser I get the entire image and the response completes.
The ISAPI extension is configured as a wildcard mapping, no caching is configured. The application pool has the 32-bits setting enabled, and runs with a domain account as identity (to access things on the back-end). I tried switching 'Enable cache' and 'Enable kernel caching' off. I tried on IIS 5.1 and 6.0 and there it works as expected.
Is there another configuration setting I am overlooking, or did I stumble upon a bug in IIS 7.5?