Concatenating a stack string with a heap string gives odd results

I am sure the following has a rational explanation but I am nevertheless a bit baffled.

The issue is with a function which creates a _TCHAR[CONSTANT], a _TCHAR*, concatenates them and returns the result.

For some reason the call to whatTheHeck() from _tmain() returns gibberish.

_TCHAR* whatTheHeck(_TCHAR* name) {
    _TCHAR Buffer[BUFSIZE];
    DWORD dwRet;
    dwRet = GetCurrentDirectory(BUFSIZE, Buffer);
    _TCHAR* what = new _TCHAR[BUFSIZE];
    what = _tcscat(Buffer, TEXT("\\"));
    what = _tcscat(what, name);
    return what;
}

int _tmain(int argc, _TCHAR* argv[]) {

    _TCHAR* failure = whatTheHeck(TEXT("gibberish);")); // not again ..
    _tprintf(TEXT("|--> %s\n"), failure);

    _TCHAR* success = createFileName(TEXT("readme.txt")); // much better
    _tprintf(TEXT("|--> %s\n"), success);

    return 0;
}

In contrast, when going with heap things work as expected.

_TCHAR* createFileName(_TCHAR* name) {
    _TCHAR* Buffer = new _TCHAR[BUFSIZE];
    DWORD dwRet;
    dwRet = GetCurrentDirectory(BUFSIZE, Buffer);
    Buffer = _tcscat(Buffer, TEXT("\\"));
    Buffer = _tcscat(Buffer, name);
    return Buffer;
}

Why the difference?

Is it because _tcscat() concatenates memory addresses instead of their contents and return purges the stack?