Open pdf only once if vimrplugin_openpdf = 1.
Now, the values of vimrplugin_openpdf mean:
0 = Don't open the pdf.
1 = Open only once (the first time that pdflatex is run).
2 = Always open the pdf.
Do "syn sync" command in Rdoc.
Update: the next release will be 1.0.