logger output to the terminal is buffered?

When I have a long running request, nothing is written to the terminal
until the request is completed (i.e. I start the server using ruby
script/server and once running, no logs appear during processing of a
request, but only after this has finished). However, if I do a

tail -f development.log

I see that the file is actually continuously updated.

Any idea about why is this happening? It was not like this before, but I
don't know what I changed in my environment to cause this change (I use
a Mac, with Leopard, and Rails 2.3.4 ).