[ruby-core:18132] Another question about IO#ungetc

Hello,

While studying the specs for IO#ungetc (http://redmine.ruby-lang.org/issues/show/400 
) we came across the following
test case:

According to the docs IO#ungetc "has no effect with unbuffered reads  
(such as
IO#sysread)" but

irb(main):001:0> file = File.open(".bashrc", "r")
=> #<File:.bashrc>
irb(main):002:0> length = File.size(".bashrc")
=> 1181
irb(main):003:0> content = file.sysread(length)
=> "export PS1=..."
irb(main):004:0> file.rewind
=> 0
irb(main):005:0> file.ungetc(100)
=> nil
irb(main):006:0> file.sysread(length)
IOError: sysread for buffered IO
	from (irb):6:in `sysread'
	from (irb):6
	from :0

$ uname -a
Darwin korobushka 9.4.0 Darwin Kernel Version 9.4.0: Mon Jun  9  
19:30:53 PDT 2008; root:xnu-1228.5.20~1/RELEASE_I386 i386

$ ruby -v
ruby 1.8.6 (2008-07-17 patchlevel 279) [i686-darwin9.4.0]

This happens in 1.8.6, 1.8.7 and 1.9. Was this changed without an  
update to
the docs or are we missing something in the test case?

Thanks.

--
Federico