Comment 18 for bug 336866

I've finally been able to duplicate this. Here's a very edited HTTP dump that shows the problem

===
GET /beta/bugs/353805 HTTP/1.1
if-none-match: "7f7f5e3c50396d650b625b8172b225368bfeecb2" (???)

HTTP/1.1 200 Ok
Etag: "3c1d2fa23419ec334f1fbaf4ca2ca94fbd2a949a"
---
PATCH /beta/launchpadlib/+bug/353805 HTTP/1.1
if-match: "34ed5fed814bac8755c4ac50c19acc76667e3bdb" (???)

HTTP/1.1 412 Precondition Failed
===

The values for If-None-Match and If-Match are totally random. They don't show up anywhere in the cache or anywhere else in the HTTP dump. In fact, even the initial requests to /beta/ have a random If-None-Match.

If I clear the cache, I don't send any If-None-Match headers, but eventually I do send a random If-Match and I get the same error.