Lately, my Chocobo (rank 11, Defender stance) has started to have some really bad issues where he will stop attacking the mob I put him on, which has cost me several maps to the same error. Today, I realized what was happening: When I cast Blizzard II on the same target my Chocobo is attacking, he stops attacking because he sees a breakable crowd control on its target.

Chocobos in Defender stance, especially ones with primary aggro, really shouldn't stop what they're doing to come give you a hug when you're fighting a mob with a massive frontal cone AoE. I'm hoping this is a bug, because if it's intentional, it's an even bigger hit to Defender viability than Choco Guard reducing their enmity generation.