To reproduce:

open /gretl/POE4data/nls_panel.gdt

start (interactive) R session
in R: 

> head(gretldata)

hours, age,  exper are lost

renamed variables
schmours=hours
schmage=age
schmexper=exper

are read ok.
Seems, there must be variables' counter and a warning message for such situations.
The predetermined names sets are different in different packages. So, one
doesn't know beforehand. Should be a warning.

!