Submitted by bin2chen, also found by oakcobalt and SpicyMeatball
Code reference: YieldWUSDStaking.sol#L468
In YieldWUSDStaking.repay(), we will calculate the amount that needs to be refunded to the user remainAmount:
 The problem is that when use call repay(), if vars.remainAmount < sd.unstakeFine, it doesnt clear vars.remainAmount to 0, which results in a refund to the user, which should be treated as unstakeFine.
For example:
unstakeFine = 10 , remainAmount = 5
As currently calculated
Over-refund remainAmount to user.
At the same time, it will also cause the contract balance to be insufficient (after collectFeeToTreasury ()) and others will not be able to repay.
thorseldon (BendDAO) confirmed and commented:
