2013/9/22 Zhouxuan <pycerl@qq.com>
http://d.puremagic.com/issues/show_bug.cgi?id=10970

That is a long-standing bug around AA value setting and opAssign, and fortunately I recently tried to fix it by determining the language semantics.
https://github.com/D-Programming-Language/dmd/pull/2539

Kenji Hara