[DatePicker] material-ui

[hyalkaf]

I have a date picker which is disabled by default. Once I change it back to be enabled, the underline style will go back to the default one. In my app, the underline will disappear all together.

Here is a jsfiddle that shows the problem: https://jsfiddle.net/432yz8qg/66/
You can see that the color on the underline changes after initial click on the button.

• Material-UI: 0.16.1
• React: 15.3.2
• Browser: Chrome

[oliviertassinari]

Closing for #4787