BUG: timeseries plot mouse-over indicates incorrect time

In pandas 0.13.1 this code produces a plot that, when "moused over", indicates incorrect dates on the 't' (x) axis, despite having the correct axis label.

``` python
pd.Series([1, 2, 3], index=pd.date_range('2014-01-01', periods=3, freq='D')).plot()
```

![screenshot](https://f.cloud.github.com/assets/5356340/2405879/8f7d2ef6-aa5c-11e3-9c68-f1383efc6b52.png)

(matplotlib version is 1.3.1)
