Make it visually clear when a filter is active.
The current implementation of the various lists in the web interface displays a small warning icon when there is a filter on a hidden column. This is good but not good enough, since a non-hidden column may still be invisible due to page width and horizontal scrolling. Eg. if the user is displaying 10+ column and has a filter in the right-most column it is almost certain that this column/filter is not visible without horizontal scrolling. This can be annoying since it may make it hard to find items.
The proposed change is that it should be visually clear when a filter is in effect. For example, by displaying some kind of icon.