The participants page in the brief layout places a checkbox in the last column of the table which gets hidden in some themes with a small center column - it also seems inconsistent with other similar tables like quiz/assignment grading pages.
I'd like to move the checkbox to the first column but would like a bit more consensus before I submit the change - this could also be considered a UI change so I'm not sure if it should land in stable branches or just the master branch - feel free to vore or add your comments to the bug: MDL-37907