# A bug in simplify_rational() function?

When I run the following

```
var('z')
( 1/z + 1/z.conjugate() ).simplify_rational()
```

on sage-8.0 / Ubuntu 16.04 LTS, I get the following answer, which is evidently wrong.

```
2/z
```

Can anyone explain why this phenomenon happens? It it a bug in simplify_rational() function?

The following dialog with the sage interpreter may highlight the implicit assumption:

I got it. Thank you very much.