helpviewer "caching"

My development system has been up for weeks. I keep a copy of helpviewer
loaded on my console #9 for easy reference.

Lately I’ve noticed that day by day it gets slower and slower whenever I try
to pop up a new page. Even if I go back to the previous page it takes 45
seconds or so.

I just dropped out of Photon and re-entered Photon and all is nice and fast
again. BTW, the rest of the system never slowed down.

Why does helpviewer slow down with age and how can I prevent it without
having to reload Photon?