Sounds like just a common mistake where people used the "stack" accidentally.

Ex:

    struct someStruct* badfunc(){
        struct someStruct toReturn;
        toReturn.a = foo();
        toReturn.b = bar(); 
        return &toReturn; 
    }

In most people's code, this would probably work...

    struct someStruct a = *badfunc();
    func2(); // This will overwrite the "toReturn" 
             // from the last call, but as long as the 
             // struct was copied before any other function 
             // call, you're probably fine though in
             // undefined-behavior land

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Either that, or you're talking about strtok (and other non-reentrant functions).