I noticed that the auto-buy feature doesn't work, if the money comes from Fool's Gold - does it only work with basic treasures? I don't see why you wouldn't want that to work with Fool's Gold or Cache, for example.
On many boards, it would even be innocuous to allow auto-buy with 2 or more buys or to play additional treasures to repay debt afterwards. But I can see that it would first be difficult to get the exceptions right and second often confusing for the player, why it doesn't work in a specific situation - so there would have to be an easy way to undo the auto-buy.