Slider breaks with theme configured with {userAgent: 'all'}

[datenreisender]

Hi,

we discovered a strange rendering problem in the slider component and could nail it down to being connected to a certain theme configuration.

Problem Description

If the theme is configured with the userAgent: 'all' (as it should be possible according to the description on Server Rendering) the bar behind the slider isn't updated anymore when the slider value is changed.

E.g. with the following code snippet

import Slider from 'material-ui/lib/slider';
import getMuiTheme from 'material-ui/lib/styles/getMuiTheme';
import MuiThemeProvider from 'material-ui/lib/MuiThemeProvider';

const App = () => 
    <MuiThemeProvider muiTheme={getMuiTheme({}, {userAgent: 'all'})}>
      <Slider defaultValue={0.4} />
    </MuiThemeProvider>

If the Slider value is changed to ~0.6 the colored and grey bar don't line up with the slider button anymore:

Correct would be (which I can get by specifying userAgent: false) if they still lined up:

## Versions - Material-UI: 0.14.4 and 0.15.0-alpha.2 - React: 0.14.7 - Browser: Chrome/OSX (48.0.2564.116) and Firefox/OSX (45.0.1)