This sounds like the converstation with the NPC got interupted by other conversation, i.e., the NPC or another NPC responded to something. A fix for this will be in the next release. Normally going back a few steps works, but if that steps requires an item you can only get once, this of course is a bit of a problem. Not much you can do about it except using an alt to get the item. If I am correct in what is happening, a bug report is not needed.