[ESS] Inconsistent M-p (previous command)

[pleydell at supagro.inra.fr]

I love the M-p functionality for recalling previous lines of code within the *R*
terminal. However, for me the function only recalls lines which were typed
manually into *R* and not for lines sent to *R* from a .R file via a C-c C-n
command. How then to reset M-p so that it recalls the last line of code that
was actually executed in *R* ?

cheers
David