I'd call that "not nice" without a doubt. Why the flag resets, I don't know. Is there, per chance, other meaningful content to the offending comment, that might be worth saving. I learned from prior discussions that even moderators can't edit a comment after it's set. The poster can, for a brief time, but then it's keep/trash as the only choice. Of course, even if the other user isn't being nice, the comments on their own will damage his reputation with other users, even if it doesn't show in his numbers. You might have to just ignore the poor soul and continue helping others where you can.
I stumbled upon a this Q in Meta AskUbuntu where a comment might explain why a flag you set disappeared without action by the mods. What @terdon comment said was
However, it's easy enough to dismiss a flag by mistake and there is no way of dismissing individual flags on the same content for different reasons (that I know of, anyway) so maybe yours was dismissed along with others that were wrong.
As the interface remains fairly consistent across SE sites, I have to presume that the same can be said of the dashboard for moderators.
Not that this helps with the comment, but it might lessen the frustration of "being ignored."
As another option, that I gathered from some meta somewhere, a last ditch effort to contact the moderators is to raise a flag for moderator flag on your own post, and explain in the custom reason area what the problem is. Sorry I can't link to that discussion, but I read too much on too many meta boards to know where to begin searching for it. An unfortunate byproduct of reading meta to try learning the site etiquette.