mv ~/.Rprofile{,.bak} mv .RData{,bak} I think the issue is a nonstandard options('prompt'). I (re)moved ~/.Rpofile and the .RData file for the working directory of the session and no longer had the blocking/endless waiting/frozen issue.
prompt as an issue also showed up when octave's default prompt changed: http://stackoverflow.com/questions/27742075/emacs-freezes-when-running-an-octave-code-block-within-org-mode
setting my prompt is now pretty complicated
.First <- function(...){ updatePrompt <- function(...) { # Emacs Speaks Stats, use default prompt if(options('STERM')=='iESS') options(prompt="> "); # Rstudio -- time but no colors else if( any(grepl("RStudio", .libPaths())) ) options(prompt=format(Sys.time(), "\n# %X\n#> ")) # command line R else options(prompt=format(Sys.time(), "\n^[[38;5;197m# ^[[38;5;27m%X^[[0;0m\n ") return(TRUE) } # add prompt if we're in interactive mode if(interactive()) { addTaskCallback(updatePrompt) } }