On team discussion lists there is a bug that might upset the more picky clients. There’s an annoying horizontal scrollbar always visible even if you have very little content:
After thorough inspection, I figured out the issue. One of the header cells of the table that shows the discussion has a position absolute.
This is an empty cell (it has a transparent image inside) and, for what I could find, it doesn't have any use.
So I just changed the position and didn't have any report of issues since.
This is the rule you can use to fix this issue:
table.ms-disc table.ms-unselectedtitle td {
position: static !important;
}