helgrind: Lock order violated in mir::client::ConnectionSurfaceMap::erase(int)

helgrind: Lock order violated in mir::client::ConnectionSurfaceMap::erase(int)

==21606== ----------------------------------------------------------------
==21606==
==21606== Thread #2: lock order "0x9258A30 before 0x9258338" violated
==21606==
==21606== Observed (incorrect) order is: acquisition of lock at 0x9258338
==21606== (stack unavailable)
==21606==
==21606== followed by a later acquisition of lock at 0x9258A30
==21606== at 0x4C2FC35: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==21606== by 0x4F9EB21: __gthread_mutex_lock(pthread_mutex_t*) (gthr-default.h:748)
==21606== by 0x4F9F171: std::mutex::lock() (mutex:134)
==21606== by 0x4FAFE86: std::unique_lock<std::mutex>::lock() (mutex:511)
==21606== by 0x4FAFC30: std::unique_lock<std::mutex>::unique_lock(std::mutex&) (mutex:443)
==21606== by 0x4FC18E0: mir::client::ConnectionSurfaceMap::erase(int) (surface_map.cpp:58)
==21606== by 0x4FAA2CB: MirConnection::released(MirConnection::SurfaceRelease) (mir_connection.cpp:159)
==21606== by 0x4FAF3E6: google::protobuf::internal::MethodClosure1<MirConnection, MirConnection::SurfaceRelease>::Run() (common.h:921)
==21606== by 0x4FD0EBD: mir::client::rpc::MirSocketRpcChannel::receive_file_descriptors(google::protobuf::Message*, google::protobuf::Closure*) (mir_socket_rpc_channel.cpp:211)
==21606== by 0x4FE7136: google::protobuf::internal::MethodClosure2<mir::client::rpc::MirSocketRpcChannel, google::protobuf::Message*, google::protobuf::Closure*>::Run() (common.h:969)
==21606== by 0x4FE7D08: mir::client::rpc::detail::PendingCallCache::complete_response(mir::protobuf::wire::Result&) (mir_basic_rpc_channel.cpp:69)
==21606== by 0x4FD195B: mir::client::rpc::MirSocketRpcChannel::read_message() (mir_socket_rpc_channel.cpp:372)
==21606==
==21606== ----------------------------------------------------------------