IIS sc-win32-status 64 when using url rewrite over https and ColdFusion

I've run into a very specific and annoying problem. It involves all of the following:

• Windows Server 2016 (IIS 10)
• Url Rewrite Module
• ColdFusion 2016
• https

When a rewrite rule is triggered to point to a ColdFusion (.cfm) page, the page seems to return fine in most browsers, but in Firefox it shows no status code in Developer Tools, and in Safari 9.1 (not in Safari 8 or 10!?) the page won't load at all. This happens only if all of the following are true:

• It's a ColdFusion page (doesn't happen with a .txt or .aspx file)
• The url is rewritten with the URL Rewrite module (e.g. /test1 rewritten to /test1.cfm)
• It is over https

When I look at the request in the IIS logs, what I see depends on the browser. It looks normal when I access with Chrome. With Firefox, it shows two requests, the first with a sc-win32-status of 64 and the second with 0. With Safari 9.1 (where the page won't load at all) it shows repeated requests, mostly with sc-win32-status=64, but also some with 22 and 1168.

Any help appreciated.