This is really annoying, and currently only seems to be happening on the PS4 since a system update, and the newly added function of when trying to purchase a game from the PStore with insufficient funds in your wallet, it will now allow auto deduction of funds to make up the difference using your selected payment type, be that CC or PayPal.

Please read on, as I'd like if somebody can check for me if the same thing is happening on their PS4, or it's just some sort of Sony F-Up for we in Aus/NZ

I usually fill my PS wallet to the MAX of AUS $250 at a time, and run it down till I have insufficient funds to buy what I want, then top it back up to $250 again.

The reason I do that is because we in AUS/NZ have to use the UK PStore to purchase from, if I top up in one large amount it saves on being totally being ripped off by bank transfer/exchange fees, as although the price for the games might appear in AUS $ at our end, adding funds to the wallet requires debit from my credit card to the PStore in UK £'s, and that attracts a flat money exchange fee from my bank of an additional $5 dollars every time I top up, regardless of the amount.

It used to be that when going to add funds to my wallet, the remaining amount in my wallet will be showing on the top right hand corner, and when going to options on how much I wanted to add to my wallet, it would show increments of $10/$50/$100 and lastly $250, this last option use to automatically deduct the amount still in your wallet and show the difference between it and $250 and add that amount instead.

Now it doesn't, it just shows $250 and doesn't deduct what's already in your wallet, and since you can't have more than $250 in your wallet at any one time, it's a catch 22 situation, I can only add funds smaller than that, which is costing me $5 every time.

To add insult to injury, after trying this several times [I kept getting CC details are wrong notices etc, even though they weren't, so deleted CC details and put them in again] I deduced it might be a PS4 system software problem since the last update, so turned on my PS3 and tried adding funds on that.

Low and behold when I went to top it up to $250, it did deduct what was in the wallet to the correct difference, and the option now showed to top up to that amount, but it still wouldn't let me to proceed with the transaction.

Little did I know that my Bank detected that someone was trying to do this [ME], so blocked my credit Card thinking something nefarious was going on.

I got a Text message from my bank alerting me and asking for conformation, which I did, but ATM at least, I still can't add any more funds to my wallet.

I'll be buggered if I'll pay double bank transfer fees because of Sony's stupidity, it's not the money so much, it's just that I HATE BANKS and pride myself on paying as little fees as possible to the A-Holes.

So could somebody have a look to see if the same situation exists for them if they already have funds in their wallet, then go to see what option shows when you select to top up their wallet to the max.
Is it deducting the difference? or Showing the Max allowed only?