Hopefully this will help find the problem.
I have the current Java version 6, revision 30.
Chrome Version (current version) 16.0.912.63
I get the reply box problem, that runs off the end of the screen.
Internet Explorer 9.0.8112 (not sure how recent this version is, as I dont use IE)
I don't have the reply box problem.
Firefox Versions 8 & 9.01 (current version).
I don't have the reply box problem.
(Edited to add IE info)