mlab.text() draws into wrong figure when using multiple figures

When using multiple mlab figures, mlab.text() always draws into the last figure instead of the figure specified via the parameter or using mlab.figure(). For example, when using

```
f1 = mlab.figure()
mlab.test_contour_surf()

f2 = mlab.figure()
mlab.test_surface()

mlab.text(0.5, 0.5, 'test', figure=f1)
```

The text appears in f2 instead of f1. The same thing happens when the last line is replaced with

```
mlab.figure(f1)
mlab.text(0.5, 0.5, 'test')
```