This was most likely caused by setting a score in between loading the top ranks section of the page and clicking "Show me more!".
Suppose the top 100 scores you have are indexed 1 through 100. The scores with indices 1 - 50 are downloaded upon opening the "Top Ranks" box and displayed. If you set a score that would be in the top 50 of your scores by pp, this will push the score at index 50 down to index 51, and then upon clicking "Show me more!", the scores with indices 51 - 100 will be displayed below the already shown ones, thus making the adjoining score appear to be duplicated.
The fact that when I view your profile now I don't see a duplicated entry makes me assume that this is the case.