Do you not make such a tacit assumption every time you index into an array (which in almost all languages throws an exception on bounds failure)? You always have to make assumptions that things stay consistent from one statement to the next, at least locally. Unless you use formal verification, but hardly anyone has the time and resources for that.
If such an error happens, that would be a compiler bug. Why? Because I usually do checks against the length of the array or have it done as part of the standard functions like `map`. I don't write such assumptions unless I'm really sure about the statements, and even then I don't.