Two parts to this:
I just recently attempted to give positive reputation to a user, and was hit with the “spread” message. Looking through my history, I noticed that I had indeed given them reputation - negative reputation, some time ago. Why should this prevent me from giving the opposite kind?
I don’t give out reputation that often, so I sometimes see this message when the last time I repped the user was over a year ago, having given maybe 10-20 since then. This seems a little bit over-sensitive to me… some users have a high density of high-quality posts, or controversial posts, and unless the system is being abused, it seems more annoying than anything else.