I've noticed some inconsistency in this lately. There are some cases like post #1298558, where a safe image of a character with visible breasts is tagged 1boy, while there are many more like post #2208969 (explicit images where the subject is tagged 1girl). In some posts, the character simply isn't counted in the gender tags at all. I think it would be helpful to have some kind of standardization for these characters.
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