Kanji radicals: Question to the radical assignment in dictionaries

I was browsing through the webpage of Japanese radicals on wikipedia (http://en.wikipedia.org/wiki/Table_of_Japanese_kanji_radicals)

I noticed

and

bot entries are referencing in the most right column to the respective other radical

I looked furthermore into the KANJIDIC2 kanji-lexicon file and it seems like these two kanjis-radicals are seemingly randomly assigned to kanjis.

According to this dictionary, the Kanji 育 has 肉 as radical (which it obviously has not, its 月). I made this observation in many places (I assumed all open dictionaries rely on the same public Kanji dictionary?)

育

80b2
16-73


130
8

Does anyone know the (historical) background of this 肉／月 radical interchangeability

Answer

Two premises:

1. Radicals are a method for indexing characters in dictionaries.


2. As an element in other characters, the form 月 can represent 肉, 舟, 丹, and 月, among others.

As you can see, these elements all look rather similar, so it's not surprising that historically they weren't always distinguished in form.

So when you see a character containing what appears to be 月, how do you know which Kangxi radical to look it up under? How would you know that 肘 and 服 are in different sections of the dictionary if you haven't learned to read these characters yet?

The editors of some kanji dictionaries have tried to solve this problem by merging radicals which are visually indistinguishable. For example, the New Nelson moves all the characters traditionally classified under 月 to 肉 (except for 月 itself). This doesn't really make sense in terms of meaning, but it makes the dictionary easier to use. This merger is especially useful for students like yourself who see 育 and say that it obviously contains 月.

You may be interested to know that in characters where 月 represents 丹, it is sometimes instead written with 円—specifically in 青 and characters containing it such as 錆, 鯖, and 睛.