I only noticed it because someone at another forum was asking for directions to remove Preview.
I thought the person wanted to remove the Preview pane when viewing the inbox so I gave directions. Other people also gave directions with screenshots and he/she kept saying it didn't work with no other information.
Several days later, I finally found out the person meant the word Preview in the title bar. A screenshot at the start of the thread would have helped all of us figure out exactly what the person wanted help with. Truthfully, I didn't notice it before this person asked for help.