When hovering your mouse over Outliner items the rows will become highlighted. Unfortunately that highlight will quite often remain after you move your mouse entirely out of that editor.
This patch fixes that, but I'm not certain this is the best way. But it is the only way I could find to do so reliably.
Blender does a good job of only directing messages to the Editor that is currently active (under the mouse), but that means there is good notification of "enter" but no reliable way to detect "leave". However, we do draw headers with an inactive color when losing focus. So this patch adds to the Outliner's header "draw" function. It checks that it is not currently active, and if not clears the TSE_HIGHLIGHTED flags from the tree and then tags the main region for redraw.