wiper/washer reserrvoir leak(?)

Hi All -

When I add fluid to the w/w reservoir, bringing it up nearly to the top, it slowly recedes down to, apparently, approximately the top of the plastic reservoir tank istself. Before I raise it as an issue (among a couple others) with the dealer, is there anything I don't know about this? Some kind of bizarre-o reserve adjunct supplementary repetidundant reservoir that for whatever reason drains the fluid off into ethereal Priusland, or something, before coming to my eventual aid? There does not *appear* to be a leak (at least not under the vehicle) when I fill it, but if there is a leak, could it be captured by the plastic whatchamajinger that makes it more aerodynamic and adds a step to the oil change process?

Anyone else notice this?

Any advice, as always, is appreciated.
Thanks,
Tim