[BitBucket user: Sébastien Jodogne]
[BitBucket date: 2016-12-12.15:15:45]

I cannot reproduce this issue. Check out the logs of your Web browser. This might be a problem with permissions, e.g. a Lua script turning Orthanc read-only:
http://book.orthanc-server.com/users/lua.html#filtering-incoming-rest-requests