I was able to pin down the villain: I remapped the help key C-h...
ehelp does not like that...
I get a *Backtrace* buffer with this content:
Debugger entered--Lisp error: (wrong-type-argument characterp [31])
char-to-string([31])
byte-code(...) ... ("/usr/share/emacs/23.0.91/lisp/ehelp.elc" .
1297))
require(ehelp)
byte-code(...)
require(term)
byte-code(...)
load("em-term")
eshell-mode()
eshell(nil)
call-interactively(eshell t nil)
execute-extended-command(nil)
call-interactively(execute-extended-command nil nil)
I am considering a default help-key mapping so that ehelp does not
complain.