For the record, links without trailing slashes are redirected to invalid (as seen from external world) host:

$ curl -v http://tools.wmflabs.org/matthewrbowker/cnrd

• Hostname was NOT found in DNS cache
• Adding handle: conn: 0x1144c10
• Adding handle: send: 0
• Adding handle: recv: 0
• Curl_addHandleToPipeline: length: 1
• - Conn 0 (0x1144c10) send_pipe: 1, recv_pipe: 0
• Trying 208.80.153.201...
• Connected to tools.wmflabs.org (208.80.153.201) port 80 (#0)

GET /matthewrbowker/cnrd HTTP/1.1
User-Agent: curl/7.34.0
Host: tools.wmflabs.org
Accept: */*

< HTTP/1.1 301 Moved Permanently
< Date: Sat, 08 Mar 2014 15:22:44 GMT

• Server lighttpd/1.4.28 is not blacklisted

< Server: lighttpd/1.4.28
< Location: http://tools-webgrid-01:4058/matthewrbowker/cnrd/
< Content-Length: 0
<

• Connection #0 to host tools.wmflabs.org left intact

This may appears to have been 'accidentally' fixed by turning ProxyPreserveHost On on the temporary apache proxies.

Appears to work for me. Thank you so much for fixing!

Reopening, behaviour seems to have reappeared following the change to a new proxy setup.

(In reply to Jarry1250 from comment #4)

Reopening, behaviour seems to have reappeared following the change to a new
proxy setup.

See bug 64058.

Unfortunately, this redirects from https to http, i. e.:

So we'll need to teach lighttpd about https (or rewrite redirects in nginx?).

Not the same issue...

That is unrelated. The proxy provides an X-FORWARDED-PROTO header which can be used by the application to construct URIs if it really must redirect between protocols.

I filed bug #64627 for the https -> http issue.