The workaround I've found is to slap her ass. Lust will work correctly after that.I seem to have found a bug.
While licking Storm's pussy, Laura came in then left. after that the little tongue disappeared and Storm's "lust" refused to go any higher. In addition, a message saying to notify Oni popped up.
This isn't game breaking or anything. I could get out of it simply by "ending the scene". It's just slightly annoying.