Right mouse button context menu items dissappearing

If I have a lister (DOpus browser) up and running for a while (minutes, hours?) most of the items on the right mouse button context menu dissappear. The only items left are the basic Windows defaults. If I close the lister and start a new one by clicking on the DOpus icon in the bottom right menu bar, the menu is restored. Any ideas as to what is happening?

Thanks!

Could you post a couple of screenshots showing the menus in both states for the same file? (i.e. Grab a screenshot just after starting, wait until the problem occurs, then grab a screenshot after right-clicking the same file again.)