Comment 1 for bug 1755554

OK, I confirmed this behavior exists with the current master. The one more odd thing is the successful PUT request with %%25ff was also logged as 409 response in the proxy-server but no any errors exist under the transaction id.

Mar 22 06:46:08 saio proxy-server: User: test uses token AUTH_tk156bef95123d40fe800845b539418eaa (trans_id txf6382b861f04463083921-005ab35130)
Mar 22 06:46:08 saio proxy-server: - - 22/Mar/2018/06/46/08 HEAD /v1/AUTH_test%3Fformat%3Djson HTTP/1.0 204 - Swift - - - - txf6382b861f04463083921-005ab35130 - 0.0106 GET_ACCOUNT_INFO - 1521701168.470243931 1521701168.480846882 -
Mar 22 06:46:08 saio proxy-server: - - 22/Mar/2018/06/46/08 HEAD /v1/AUTH_test/c2%3Fformat%3Djson HTTP/1.0 204 - Swift - - - - txf6382b861f04463083921-005ab35130 - 0.0198 GET_CONTAINER_INFO - 1521701168.481514931 1521701168.501288891 0
Mar 22 06:46:08 saio proxy-server: User test:tester has admin authorizing. (txn: txf6382b861f04463083921-005ab35130)
Mar 22 06:46:08 saio proxy-server: - - 22/Mar/2018/06/46/08 GET /v1/AUTH_test/c2/%2525ff HTTP/1.0 499 - Swift - - 70 - txf6382b861f04463083921-005ab35130 - 0.0245 VW - 1521701168.505810976 1521701168.530276060 0
Mar 22 06:46:08 saio proxy-server: User test:tester has admin authorizing. (txn: txf6382b861f04463083921-005ab35130) (client_ip: 127.0.0.1)
Mar 22 06:46:08 saio proxy-server: 127.0.0.1 127.0.0.1 22/Mar/2018/06/46/08 PUT /v1/AUTH_test/c2/%252525ff HTTP/1.0 201 - curl/7.47.0 AUTH_tk156bef951... 4 - - txf6382b861f04463083921-005ab35130 - 0.0935 - - 1521701168.469007015 1521701168.562541962 0
Mar 22 06:46:08 saio proxy-server: STDERR: 127.0.0.1 - - [22/Mar/2018 06:46:08] "PUT /v1/AUTH_test/c2/%2525ff HTTP/1.1" 201 314 0.096156 (txn: txf6382b861f04463083921-005ab35130)

I'll dive into deeper what pass was taken in the versions_writes middleware...