Extra turn bug?

[GTea]

In several fights I've noticed that the enemies' turn seem to be skipped occasionally. This was the most apparent in the Behemoth fight at the Colosseum where he attacked once, and then proceeded to do nothing for several turns until I finally defeated him. There was zero indication that an attack was attempted and missed, he just simply stood there.

Is this a bug or a feature of the game that I don't understand?

[GPI_Flush]

Were you using the Sleep Blade? I've noticed while I was fighting Hill Gigas that they were skipping turns as well and I assumed that it was because of the Sleep Blade, however you wouldn't be able to tell because there's no visual effect of it working.