FT changed their subs commissions after all the complaints about DPC (and about their monthly subs packages, which essentially are nothing else but credit packages, but used to pay just subs royalties). Now you get 20% of what the buyer paid (25% if opted into DPC).

Do get 5 Credits the buyer must have paid 25 for the one image.

On the German site they sell those monthly "subscriptions" for 25 � for 5 images.

So if a buyer just used one of those, that might lead to such a sale.

That assumes that FT really takes into account how much of his quota a buyer has used. But that would mean that they can only inform you about the sale once the validity of the credit pack has expired, so no real time reporting for those subs...

Many assumptions, but the only way I can come up with a 5 credit sub sale.
The biggest I had was a little over one credit, 1.07 to be exact.