It sounds like the NPC is repeatedly running a dialog package, and the conditions of the topic of the package are such that any infos for the topic are disabled, so it will zoom and the text area will be blank. After the dialog package completed once, did you set a variable to disable it?
Yeah that sounds about what's going on. I'll check now.
I figured, that the package would check conditions before trying to converse with the PC, but yeah computers are picky like that =P