Welcome to the forum.
A lot of browser issues were fixed through RoboHelp 7 and 8. I suggest you download the trial and install it on another machine. Do not install it on your X5 machine. That way you will find out if the problem is fixed.
405 is a recent version so I am not surprised an old version of RoboHelp has problems.
See www.grainge.org for RoboHelp and Authoring tips