Thanks for the report, I've got a fix! The issue is mildly complicated, so bear with me for the explanation.
OrCosts check the individual options to see if the ActionCosts are payable. For example, for for Spark Harvest, it checks whether you are capable of sacrificing any creatures or planeswalkers. If you can't, it doesn't offer that option - and if there's only one option left, it auto-picks it.
Well, it turns out we weren't cleaning up those "we're determining whether this cost is payable" facts for the mana costs. And cost adjustment rules like that of Kasmina specifically check that we're not determining cost payability for them to apply.
So the fix is to clean up the DetermineCostPayability facts when checking whether an OrCost is payable. Hope that makes sense! Fix will go live with the next engine patch. #wotc_staff