How to make C-c C-o preserve the command line?

[Alejandro Munoz del Rio]

Dear ESS-help members,

I run ESS 5.1.24 in WinXP and WinME. On both platforms, C-c C-o deletes the
output from a given command and replaces it with "***output flushed***".
However, on XP the command line itself is deleted along with the output,
whereas on ME the command line is preserved. I find the latter more convenient
for re-running commands. Thus: 

How can I make C-c C-o preserve the command line that generated the deleted
output? As far as I can recall I haven't customised anything to get different
behaviour.

alejandro