When you exchange Gold bars/nuggets at the Britannian mint and all partymembers don't have enough capacity to carry all the gold coins (but enough to hold some) you will lose gold coins. Same as in the original.
When you have hackmover enabled the same happens in Exult. The original put all the gold into the Avatar's backpack.
I'm attaching a savegame for both Exult and the original game.
tracked in https://github.com/exult/exult/issues/872