StringIO#ungetc returns dupes in Ruby1.9?

[David Masover]

First, I apologize if this was a known issue -- couldn't find any mention of
it in English. Seems to happen only in Ruby 1.9, and I've only tried with the
version that comes with my Ubuntu repositories:

$ ruby1.9 --version
ruby 1.9.0 (2007-12-25 revision 14709) [x86_64-linux]

IO#ungetc is supposed to push one character back onto the IO stream, such that
it will be at the beginning of the next read. I think the idea is to let
one "peek" at upcoming characters -- or at least, that's how I'm using it.

And that works fine, in Ruby 1.8, and on Files, but not on StringIOs in Ruby
1.9:

$ irb1.9
irb(main):001:0> require 'stringio'
=> true
irb(main):002:0> s = StringIO.new('what')
=> #<StringIO:0x007f5555306428>
irb(main):003:0> s.getc
=> "w"
irb(main):004:0> s.getc
=> "h"
irb(main):005:0> s.ungetc 'h'
=> nil
irb(main):006:0> s.getc
=> "h"
irb(main):007:0> s.getc
=> "h"
irb(main):008:0> s.getc
=> "a"
irb(main):009:0> s.getc
=> "t"
irb(main):010:0> s.getc
=> nil

To clarify: The 'h' was read once, so it should have been off the stack, so to
speak. It was then "unread", and read again... Then again. Even stranger
things happen with rewind after ungetc.

This is a bit annoying, as it's the whole reason I was using StringIOs in the
first place.

Can anyone duplicate this with the latest 1.9?