This probably indicates the "waste ink pad" is getting full. Waste ink comes from print-head cleaning, purging when print-head parked and/or tank change ... also from "over-spray" from borderless prints. May be other causes, but I think those are the main reasons.
If you let the ink pad get over-full ... which is A LOT of printing ... you can get nasty used ink where you really don't want it. To me, when an entry-to-mid level, non-professional printer fills the waste-ink pad, it is "fully depreciated" and approprate to retire.
