Why would an http-client request fail with this 400 error when wget and firefox work fine?

http-client output from WebConstraintsUnitTestCase.testGetAccess test:
217 [main] DEBUG org.jboss.test.util.web.HttpUtils - Connecting to: http://getUser:getUserPass@localhost:8080/web-constraints/restricted/get-only
221 [main] DEBUG org.jboss.test.util.web.HttpUtils - RequestURI: http://localhost:8080/web-constraints/restricted/get-only
240 [main] DEBUG org.apache.commons.httpclient.HttpConnection - Open connection to localhost:8080
244 [main] DEBUG httpclient.wire.header - >> "GET /web-constraints/restricted/get-only HTTP/1.1[\r][\n]"
244 [main] DEBUG org.apache.commons.httpclient.HttpMethodBase - Adding Host request header
259 [main] DEBUG httpclient.wire.header - >> "User-Agent: Jakarta Commons-HttpClient/3.0.1[\r][\n]"
260 [main] DEBUG httpclient.wire.header - >> "Host: localhost:8080[\r][\n]"
261 [main] DEBUG httpclient.wire.header - >> "[\r][\n]"
264 [main] DEBUG httpclient.wire.header - << "HTTP/1.1 400 No Host matches server name localhost[\r][\n]"
266 [main] DEBUG httpclient.wire.header - << "Server: Apache-Coyote/1.1[\r][\n]"
266 [main] DEBUG httpclient.wire.header - << "Transfer-Encoding: chunked[\r][\n]"
266 [main] DEBUG httpclient.wire.header - << "Date: Wed, 05 Dec 2007 20:21:51 GMT[\r][\n]"
266 [main] DEBUG httpclient.wire.header - << "Connection: close[\r][\n]"
272 [main] DEBUG org.jboss.test.util.web.HttpUtils - responseCode=400, response=No Host matches server name localhost
272 [main] WARN org.apache.commons.httpclient.HttpMethodBase - Going to buffer response body of large or unknown size. Using getResponseBodyAsStream instead is recommended.
272 [main] DEBUG org.apache.commons.httpclient.HttpMethodBase - Buffering response body
272 [main] DEBUG httpclient.wire.content - << "0"
272 [main] DEBUG httpclient.wire.content - << "[\r]"
272 [main] DEBUG httpclient.wire.content - << "[\n]"
272 [main] DEBUG httpclient.wire.content - << "[\r]"
272 [main] DEBUG httpclient.wire.content - << "[\n]"
273 [main] DEBUG org.apache.commons.httpclient.HttpMethodBase - Should close connection in response to directive: close
273 [main] DEBUG org.apache.commons.httpclient.HttpConnection - Releasing connection back to connection manager.
273 [main] DEBUG org.apache.commons.httpclient.HttpMethodBase - Default charset used: ISO-8859-1
273 [main] DEBUG org.jboss.test.util.web.HttpUtils -

wget output:
[starksm@succubus testsuite]$ wget -S --http-user=getUser --http-passwd=getUserPass http://localhost:8080/web-constraints/restricted/get-only
-12:26:36- http://localhost:8080/web-constraints/restricted/get-only
=> `get-only'
Resolving localhost... 127.0.0.1
Connecting to localhost|127.0.0.1|:8080... connected.
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Pragma: No-cache
Cache-Control: no-cache
Expires: Wed, 31 Dec 1969 16:00:00 PST
X-Powered-By: Servlet 2.5; JBoss-5.0.0.Alpha (build: CVSTag=HEAD date=200606261952)/Tomcat-6.0
Content-Length: 79
Date: Wed, 05 Dec 2007 20:26:36 GMT
Connection: keep-alive
Length: 79

100%[===================================>] 79 -.-K/s

12:26:36 (6.28 MB/s) - `get-only' saved [79/79]