Modify opacity:

Enable "play" button when real time is disabled, so if you want to
enable real time you should press "play" button.
When real time is running and you want to pause it, you'll have to press
"pause" button.

Seems to me like a normal behavior.

Real time enabled (play button disabled)
![enabled](https://f.cloud.github.com/assets/537305/2385285/b00be47e-a91b-11e3-8206-75e9cea65242.png)

Real time paused (play button enabled)
![disabled](https://f.cloud.github.com/assets/537305/2385289/b674bbe2-a91b-11e3-85e3-6a0c98bf10cf.png)