Why central builds are performed on 10.1 with broken/different compared to 10,3 compiler?

[Yuri]

I regularly get the fallout messages for my net-im/ring-daemon port. It 
breaks on 10.1 with the c++11 -related message:

In file included from /wrkdirs/usr/ports/net-im/ring-daemon/work/ring-daemon-56ec56f/src/manager.h:45:
/wrkdirs/usr/ports/net-im/ring-daemon/work/ring-daemon-56ec56f/src/account_factory.h:121:107: error: chosen constructor is explicit in copy-initialization
         std::map<std::string, std::function<std::shared_ptr<Account>(const std::string&)> > generators_ = {};
                                                                                                           ^~
/usr/include/c++/v1/map:838:14: note: constructor declared here
     explicit map(const key_compare& __comp = key_compare())


net-im/ring-daemon doesn't break on 10.3 system though. It has USES=compiler:c++14-lang.

There are two questions:
1. Why clang36 works differently on 10.1 and 10.3?
2. Should 10.3 be used for central builds then?

Yuri