Currency Exchange Ratio bug

I've been executing arbitrage trades in a very slow moving currency, so I've observed a bit of behaviour that seems incorrect/wrong. It's to do with the exchange always trying to give the player a deal that matches their ratio or better.

Lets say I'm selling 85 items for 18 exalts (4.72222 ratio) vs someone selling 47 items for 10 exalts (4.7 ratio). I'm at the top of the order chain, undercutting all other offers and supposed to be "making a little less".

I observed many buying 23 of my item for 5e. (4.6 ratio) and 47 for 10e (4.7 ratio). I don't know why they're buying this amount, possibly the auto-suggest is giving them this number.

After executing that trade, my items no longer match my ratio and it kicks my order off.

BUT, I made the good 4.6 ratio deal, AND beat my 4.7 ratio opponent to the trade. Their number of items listed remains unchanged. It's also beating my 4.62 ratio opponent. I also have made 4.7 ratio trades even before my 4.7 opponent did.

It seems like the correct way should work in reverse, eating from the closest matching ratio, rather than the top of chain, otherwise you can constantly relist at these odd ratios for the faster trades, while not actually undercutting.