@armingrudd to be honst I cannot exactly recall when the problems started. There was this debate around KNIME 4.5 - where there were some changes and some cases worked.
I have rewritten a workflow to use the R community nodes since I was experiencing problems with the R nodes (on Mac). But it was difficult to pin them down.
I have started an article about visualizations and R with KNIME but stopped because I lacked the energy to go thru convincing someone that there is a problem 
- so if you might want to take an additional look that would be great. Not doing much with R at the moment.