It sounds like a bug in the expansion manager (an unmanaged component of Visual Studio). It is responsible notably for Visual Studio's snippet expansion feature.

You could track the registry, for example, this key:

HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\11.0_Config\Languages\CodeExpa‌​nsions

and check all the sub keys, see if something looks bad, the directories, or even the .XML files (containing snippet configurations) pointed at. You can also use SysInternals' ProcMon tool to monitor what's going on.

Ultimately, you could also kill all these keys and launch a repair...

It's also possible to report the bug to Microsoft here: Connect site for Visual Studio but if it's not easily reproducible, it may not be fixed in a near future.