The behavior you are seeing is being caused by a code snippet. Snippets can be activated by typing the snippet shortcut followed by a tab. Visual Studio 2012 comes with several code snippets pre-installed for several different languages. For the C++ language there a default snippet with a shortcut of {
which expands to:
{
}
The default snippets can't be disabled easily through the default GUI, however you should be able to remove the snippet file which is located at (for English language):
%VSInstallDir%\VC\Snippets\1033\Visual C++\{.snippet
I believe there are other extensions out there for managing snippets as well.