If we use the scenario in the King Neptune case, as long as the bets placed did not dip into the use of funds from the bonus then it can be argued that the winnings are derived from the deposit only.
As I said, KN went out of their way to show that even under the best possible scenario for the player, the player did not meet any conditions.
The issue here is whether or not you are using your deposit BEFORE your bonus - I believe that this whole concept is misunderstood by both players and casinos alike.
First of all, in a land-based casino, you will ALWAYS be using a bonus coupon at the same time as a real bet (for example, "This coupon entitles you to 2x payout on any single play). I have never ever seen a circumstance where any type of bonus can be played without real funds being present.
Let's take a land-based slot club scenario - you get cashback or bonus points on your card, and activate the card. You are asked whether you wish to play your bonus money or NOT. Some people actually prefer to accrue it until it reaches a certain level. Some people immediately play with the bonus money, which is then used BEFORE real money.
Nowhere have I seen a scenario where real money comes into play first before a bonus except in the sole case where you are talking about two different accounts/wallets/whatever. The slot club card is one wallet - you cannot put real funds on that card. Your wallet is one wallet - you cannot put bonus funds into that wallet unless it is able to be turned directly into real funds.
In an online scenario, the two account system has already proven unpopular. So throw out that idea, even if it DOES make sense.
The only reasonable way to consider these online situations is as if the bonus is being played at the same time as the real funds in the appropriate proportion as I have described above. You cannot be playing with real funds before bonus funds, it makes absolutely no sense, unless you REJECT the bonus funds.
Actually, I fail to see how the casino was disadvantaged if they had deemed the player to have deposited in euros. He deposits in pounds and gets winnings in euros. Casinos should welcome these players with open arms because they would lose their deposits in pounds.
Unfortunately, that's nonsensical. No one in their right mind deposits pounds with the INTENTION of winning Euros.
Just trying to take advantage of the situation IMO.
I will again vouch for KN in saying that they had absolutely no intention of taking advantage of the situation. I cannot speak for Palace Group because I do not know the circumstances as well - but I think that, except for the unclear wording which has since been modified, it's quite clear that the player attempted to take an unfair advantage by ignoring a term which was already present in the first place - that is to deposit in the currency of his residence.