ActiveRecord::Errors#full_messages changes in 2.3.4

After upgrading our application from Rails 2.3.2 to 2.3.4 all our
error messages appeared as "{{attribute}} {{message}}" (literally).

Since we noticed this problem short before a release and hadn't enough
time to look deeper into it we fixed it by using the "old"
full_messages method that was present in 2.3.2

So today I started reading up on what exactly has changed, but
currently I've hit the wall and have no idea what it was. I've read a
couple of bug reports and looked at the commits but I couldn't make
anything out of it.

Our applications uses I18n and I know the recent changes might have
something to do with that.

Is there anybody that could explain to me what has changed between
2.3.2 and 2.3.4 concerning error messages on your models?

We could go with the "fix" we have now, but I really would like to
understand the changes and do it the "right" way. We are using Rails
for a reason after all..

Thanks a lot,