You can always write the wrong code if you want it enough. But hopefully a warning would have prompted someone to think harder about this flow.
IMHO the goal is usually for the compiler not to make these decisions but to provide the tools for the APIs people build to make them. That's kind of passing the buck, though.
I guess in this case the core problem is that the API for these I/O calls has no representation in the type system for what's happening to the buffer. Proxying it as ‘the programmer must think about this code path’ is a reasonable best-effort but, evidently, sometimes inadequate.