[ BUILD # : 200903250219 ]
[ JDK VERSION : 1.6.* ]

When stepping over an operation in the debugger with the Variables
window showing, the variables window flashes rapidly while the
debugger steps through the process behind the scenes.

Easy way to reproduce,

1) Create a new Rails Project that uses a gem (not Rails)
2) rake rails:freeze

3) Now put a breakpoint in vendor/rails/railties/lib/initializer.rb
on the first line of add_gem_load_paths 

4) Now put a breakpoint in vendor/rails/railties/lib/initializer.rb
on the 'require "rubygems"' line inside the "unless
@configuration.gems.empty?" block

5) Debug your application.  When it stops on the first breakpoint
open the Variables window.

6) Now debug by stepping over each instruction.  

The first step on the "unless @configuration..." line demonstrates
the flickering.