yes - interesting arrangement isnt it.
I wonder what the thinking is here - myabe the baffles are for strength - since it's gotta handle 7lbs or half a bar...not small - 1000lb/ft2 (5tonnes/m2), ...and its plastic - most cheap sources are only good to 170-200F before significant strength loss. So methinks they are for stength and the holes to allow a simple single point fill for both circuits.

Okay - the following - are ramblings - but hey - there maybe someone whos bored enough out there to read it....I'm bored enough to write it...gotta keep the free expression rolling!
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Since heat rises and there is little cooling in the resevoir, heat will rise from the engine circuit and push liquid up from the engine circuit/radiator through the bottom entry point (70ml per 40F). This will intermix with the reservior bulk, but the charge air circuit isnt calling for fluid until it begins to cool*.
Hot fluid stays up the top - as per hot air rises....
When it does begin to cool (20ml per 40F) subsequently drawing that 20ml back into the system. Hey that's not enough to even get down the tube to the flowing charge air circuit.....hmmm...

Maybe explains why after 3 days (30miles) of replacing the Engine Coolant with blue, my Charge Air coolant was still green from the previous fill. of course racing is a different story. So this can develope a cycle between periods of WOT and off obviously.

And of course if you had different solutions in each circuit - you wanna keep 'em seperate - hence the seperation tube I'm considering.