$ cat >foo
bar
$ ruby-1.8.0 -e 'p IO.readlines("foo", nil)'
["bar\n"]
$ ruby-1.8.1 -e 'p IO.readlines("foo", nil)'
-e:1:in `readlines': Interrupt  from -e:1
$ ruby-1.8.1 -v
ruby 1.8.1 (2003-12-25) [i686-linux]

I had to interrupt the second one.

There's nothing about readlines in the ChangeLog. What happened?

I know I can use File.read, but I had left IO.readlines in some places 
for backwards compatibility.