User blog comment:Miskos3/Fairy Tail Chapter 367: Jellal vs. Oracion Seis, Review/@comment-4223231-20140117220440/@comment-7418318-20140117224450

Considering how he's reacting embarrased the first moment he saw her naked, but then reacted completely nonchalantly when he later turned around to face her (before he caught the kick) I'd say it's exactly this "novelty" thing.

And that he is also naked might also contribute to his embarrasment, since whenever he saw Lucy almost or completely naked, he was either wearing clothes or had his lower half below the water-level, so any physical reaction would be hidden from sight.

Or it could mean that he's so comfortable around Lucy, that it's not bothering him with her and that he's not as comfortable around Lisanna.

Or it was just done for comical purpose without any deeper meaning.