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 ).