How did you identify that there was just one like? If you just browsed the table directly, you may have missed the other one as they won't necessarily be in order. You likely need to search by the post ID.
There is a unique constraint in place in MySQL that physically prevents the same post twice; the double news feed could be from a like/unlike.
If you did the like/unlike, that would rebuild the like cache which is reading the data fresh from the DB.