Possible bug in RoR-2.3.8 wrt migrations

I have opened this ticket:

https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/4891-rails-238-dbmigrate-gives-undefined-method-length-for-any_indexsymbol

The problem does not occur with RoR-2.3.5

Basically, wherever I have defined an index in a migration the rake
db:migrate task throws this error:

<pre>
-- add_index(:sessions, :session_id,
{:unique=>true, :name=>:idxr_sessions_session_id})
rake aborted!
An error has occurred, this and all later migrations canceled:

undefined method `length' for :idxr_sessions_session_id:Symbol
</pre>

It seems it expects the index name to be a string, does it work if you
use a string?