It seems very strange to me that the 終止形 and 連体形 of a word like 食べる used to be 食ぶ and 食ぶる, Vovin says in his A REFERENCE GRAMMAR OF CLASSICAL JAPANESE PROSE that 食べ is the stem to which -u, -uる and -uれ are attached to. 食be + -uる -> 食beuる -> 食ぶる. So my question is how exactly did 食ぶる become 食べる again? Since 食ぶる is already the contracted form used in all situations. Is it due to dialectal difference like how in Eastern Japan -(a)ない was already present but was just never written down except in some scant poetry?