Clearing xterm clipboard/selection/cutbuffer

[Ras Far]

Hi,

I'm having difficulty clearing the clipboard/selection/cutbuffer.  Any
combination of xsel -[cd] -[psb] fails to clear a selection made in
xterm using standard left-drag.

I can SET the selection with xsel -i but it cannot be empty, so the
best I can do is replace the current selection with a space.  Not
terrible, been doing that manually for a long while, after each
selection, since accidental pastes can be disastrous.  But I'd like it
to be really empty, the way it is when first start X, prior to having
made any selections.

I've also tried xclip, xcutsel, and changing the xterm
selectToClipboard resource to true...  Even tried hacking xsel.c
source but had no luck there either!

My system is Ubuntu 11.04 (GNU/Linux 2.6.38-13-generic i686), twm,
X.Org X Server 1.10.1.

Can anyone suggest what's going wrong with xsel -c/-d?

Kind Reg'ds,
Ras