clarify that not all errors are observed

src/libstd/io/buffered.rs

@@ -366,8 +366,9 @@ impl<R: Seek> Seek for BufReader<R> {
 ///
 /// It is critical to call [`flush`] before `BufWriter<W>` is dropped. Though
 /// dropping will attempt to flush the the contents of the buffer, any errors
-/// that happen in the process will be ignored. Calling ['flush'] ensures that
-/// the buffer is empty and all errors have been observed.
+/// that happen in the process of dropping will be ignored. Calling ['flush']
+/// ensures that the buffer is empty and thus dropping will not even attempt
+/// file operations.
 ///
 /// # Examples
 ///