I hope it's just me but seems like xCHM will empty the clipboard when closed.
If it's not me, why?
If by "it will empty the clipboard when closed" you mean that text that you've selected and copied from xCHM is no longer available for pasting, that seems to happen with all the applications I've tested with on my Gentoo Linux (Firefox, XEmacs, and others).
I guess the questions would be:
1. which xCHM (the Linux, Windows or Mac version)?
2. does it empty everything in the clipboard, or only what you've copied from xCHM?