User blog comment:Omega natsu2/Chapter 353: Exorcism, Predictions./@comment-7418318-20130927110546/@comment-7418318-20130927112634

It's possible (even likely if you ask me) that they didn't fight since the last chapter.

The stopped when Natsu went all-out on the eyeball bird, right after that Atlas Flame's spirit appeared. Those two highly skilled mages would surely have noticed the magic power (not to mention seeing the FREAKING HUGE DRAGON SHAPED FLAME which must have been visible from very far away) and then when the flame disappeared and they got ready to fight again, the ice started to melt.