In Snagit 12 you need to click on gear icon to the right of the red capture button and go to preferences. Then choose the option shown below.
The revised on-screen floating user interface introduced in Snagit 11.2 is called OneClick. Please take a look at the link below for a tutorial on OneClick, this includes instructions on disabling the feature if you desire. (Open Snagit > Select “Turn off OneClick” in the “Quick Launch” section.)