When playing a bot match, if you enable a Wall type creature, or a creature with Defender, to attack, Sparky will not block the attacking creature with defender, even if the bot would lose as a result. If Sparky has very little life points and creatures on the field, it will block attacks, if able, to stay in the game. But if the attacker has Defender, Sparky will not block, even if it's creatures are able, up to losing the game. An example of this is Demon Wall, which has Defender, but can attack if it has +1/+1 counters on it. This creature can give itself counters, or another source could give it counters.

I'm playing on Windows PC, not Steam.

I would expect the bot to recognize that the creature with Defender can and will attack, and deal with it appropriately, especially when defending to not lose. It blocks othe creatures under the same conditions, and should know to do the same with this type of interaction.

No workaround found yet.