OK, just found the solution myself. As I was suspecting, it was hiding elsewhere in the options: Tools->Options->Text Editor->C/C++->Code Style->General->Comments->Continue single line comments = Uncheck. The same can be accomplished by higher-level Tools->Options->Text Editor->C/C++->Code Style->General->Comments->Insert existing comment style at the end of new lines when writing comments = Uncheck, but I suspect this will clip even more functionality, so the first option is minimally invasive.