Full-screen Applications Occasionally Tab Out When Pressing Mouse Button 5

[Tastybird { 'v' }]

Basically the title. The most direct example of this I can think of is when I'm playing a game, for example, League of Legends. I have certain abilities on my mouse buttons, and seemingly at random, pressing mouse button 5 will tab out of the game. How might I figure out how to solve this problem?

 

I can't remember the name of the application, and I can't find it after trying to look it up, but there's a Windows application that shows you a log of all the previous processes on the computer, such as automatic updates and whatnot. If someone could remind me of the name of that application, it would help me to give more information on the problem.