The instructions for Rcmdr say that if the cursor in the R script window is on an R command and we click SUBMIT, the command is executed. That often works, but not always. When it fails (such as when modifying parameters in xyplot(), for example), SUBMIT still works if I select the entire line of command(s), but it fails if the line is not selected and only the cursor is placed on the line.
R 3.6.1, Rcmdr: 2.5.3, Linux Mint-XFCE 19.1, kernel 4.15.0.55