Glitch with multiple refunds against a purchase

Hi
I’m having problems balancing a refund against an expense/ purchase, but only in certain situations…

For example, if i have a £100 purchase which is matched to the bank feed, and I also have a £100 refund, I can do this and the refund balances against the purchase no problems. 1 purchase to one refund works fine…

But if i have a £100 purchase, and then a £50 refund, a £30 refund and a £20 refund against this purchase, the first 2 refunds (£50 and £30) will come off fine, but the final £20 one wont… Even if there is that exact amount left on the original purchase. I get an error stating;
“This purchase has already been refunded, please select a different purchase”.

It’s only ever the last refund though, whether I have 2, 3, 4 or 5 refunds against this purchase. But as i say, if its 1 refund to 1 purchase, its fine. Just always an issue with the last refund when there are multiple.
Can anyone advise on this and if its a glitch, can it be looked into? Thanks