Logging progname with Rails differs from Ruby

There are some differences in how Ruby 1.9.3-p198 and Rails 3.2.3
handle logging a program name.

# Standard Ruby Logger:
logger.error('program name'){'message'}
logger.error('program name'){exception}

# Rails:
Rails.logger.error('message', 'program name')
Rails.logger.error(exception, 'program name')

If trying to switch between the two, using the standard logging format
with the Rails logger, I find that Rails ignores the block and logs
the 'program name' as the message instead.

Attempting to use the Rails format in IRB errors out with:
ArgumentError: wrong number of arguments (2 for 1)

Is this intentional or is it a bug? I haven't seen anything logged on
it anywhere, but may not be looking in the right place.