Walking Bulwark
Card Stats & Details

• Mana Cost: {1} (1 colorless)
• Type: Artifact Creature — Golem
• P/T: 0/3
• Keywords: Defender
• Activated Ability (Sorcery Speed, Cost {2}): Target a creature with defender. Until end of turn, that creature gains haste, can attack as though it didn't have defender, and assigns combat damage equal to its toughness rather than its power

The Bug --->

paying 2 mana to give itself the buff flat out eats the mana and does nothing......

However paying ANOTHER 2 mana for a total of 4 mana on the SAME TURN now properly gives Bulwark's buff to itself.

It has zero problems buffing other creatures for only 2 mana. When it comes to itself it needs a total of 4 for no good reason at all.