The "pasting of blanks symptom" is a little strange, but there is an RM setting that might solve your problem. It may be found at Tools->Program Options->Use plain text when pasting to notes.
Here is a little history lesson about RM and its predecessor which was called Family Origins. For many years, the only kind of paste that RM had was an unformatted paste. That meant that the pasting always worked well, but it also meant that you lost any formatting such as bold or italics. The ability to paste with formatting was much wished for by RM users, and one day the paste with formatting feature was added. But there were huge complaints from users because some users found that the formatted paste gave them all kinds of crazy results and that the only solution was to paste somewhere else than RM and then copy and paste it a second time into RM. The second copy and paste worked because it removed the formatting. That is what you are doing with TextWrangler or Textedit.
As a result of the user complaints about formatted paste, RM provided an option whereby formatted paste could be turned off and RM would go back to doing unformatted paste. That's the option I'm suggesting that you might want to use.
I don't know what percentage of RM users turn off formatted paste but it's probably pretty high. I personally find formatted paste to be absolutely invaluable and I leave it turned on all the time. For whatever reason, I don't seem to have too much trouble with it. But on those rare occasions where it does cause a problem, I simply paste into Notepad (lots of other programs work as well) and then copy and paste out of Notepad and into RM to remove the formatting. You just need to set the option in whatever way best meets your needs.
I think a slightly better way to handle the user interface would be to get rid of the option entirely and have the default to be paste unformatted. Then for users like me who usually prefer paste formatted, provide a right click option for the paste that would allow me to select paste formatted. But that's not the way it works, and changing the way it works at this point would probably just cause confusion.