[BUG?] rake db:test:clone when index multi columns

I tried to clone my DB and got an error : (Mysql 5 / Rails 1.2 / OS X)

rake aborted!
Mysql::Error: BLOB/TEXT column ‘description’ used in key specification
without a key length: CREATE INDEX title_description ON propositions
(title, description)

but the index key length exists in my dev DB…

(from Mysql => title_description INDEX title 25 description
50)

seems to taken in account at all…

rake db:schema:dump
=> add_index “propositions”, [“title”, “description”], :name =>
“title_description”
in the schema.rb

is it a bug ?