Intermittent IO.popen "Bad file descriptor" failures upon IO#close when using read+write mode on JRuby 1.7.3.

backtrace.txt

% jruby -J-Djruby.backtrace.style=raw popen.rb
using r...
using r+...
IOError: Bad file descriptor
            getStackTrace at java/lang/Thread.java:1567
         getBacktraceData at org/jruby/runtime/backtrace/TraceType.java:171
             getBacktrace at org/jruby/runtime/backtrace/TraceType.java:39
         prepareBacktrace at org/jruby/RubyException.java:215
                 preRaise at org/jruby/exceptions/RaiseException.java:214
                 preRaise at org/jruby/exceptions/RaiseException.java:195
                   <init> at org/jruby/exceptions/RaiseException.java:112
        newRaiseException at org/jruby/Ruby.java:3654
  newIOErrorFromException at org/jruby/Ruby.java:3585
                 finalize at org/jruby/util/io/OpenFile.java:399
                  cleanup at org/jruby/util/io/OpenFile.java:318
                   close2 at org/jruby/RubyIO.java:2074
                    close at org/jruby/RubyIO.java:2052
                     call at org/jruby/runtime/callsite/CachingCallSite.java:134
                       ls at popen.rb:5
                       ls at popen.rb:5
                     call at org/jruby/runtime/callsite/CachingCallSite.java:168
                   (root) at popen.rb:12
                   (root) at popen.rb:12
                    yield at org/jruby/runtime/CompiledBlock19.java:139
                    yield at org/jruby/runtime/Block.java:130
                    times at org/jruby/RubyFixnum.java:273
             cacheAndCall at org/jruby/runtime/callsite/CachingCallSite.java:316
                callBlock at org/jruby/runtime/callsite/CachingCallSite.java:145
                 callIter at org/jruby/runtime/callsite/CachingCallSite.java:154
                   (root) at popen.rb:12
                   (root) at popen.rb:12
                runScript at org/jruby/Ruby.java:815
                runScript at org/jruby/Ruby.java:808
              runNormally at org/jruby/Ruby.java:679
              runFromMain at org/jruby/Ruby.java:528
            doRunFromMain at org/jruby/Main.java:390
              internalRun at org/jruby/Main.java:279
                      run at org/jruby/Main.java:221
                     main at org/jruby/Main.java:201

popen.rb

#!/usr/bin/env jruby

def ls(mode)
  io = IO.popen('ls', mode)
  io.close
end

puts "using r..."
800.times { ls('r') }  # always succeeds

puts "using r+..."
800.times { ls('r+') } # usually fails