The problem with small cameras....
This doesn't just pertain to the Fuji, but all small cameras with lots of control buttons.
There isn't a lot of room to place your fingers. Putting them in the wrong spot, over a button, can cause inadvertent button presses and setting changes.
I've done this with other cameras as well, but, the Fuji does have one unique feature that makes this easier to do, it's OVF.
The OVF doesn't tell you when you changed a setting and it gives you no idea of what the output looks like until you move your eye back to the screen and start reviewing your shots.
Yesterday I took an entire session of photos with the WB set to custom.
I sometimes think it would be nice if there were a settings lock button, like there is on an MP3 player.