I encountered this problem and there was no clear explanation about how to work around this bug.
The latest version of R (v. 3.1.2) for OS X Mavericks freezes in Yosemite whenever I try to save a file which is written using R's internal editor. It also freezes when you try to source
a function.
Edit: This was supposed to be a self-answered question, but I found a better answer, so I marked that as the answer.
I have run into the same problem. I haven't tried Metallica's answer but found the problem has 95% disappeared after installing the latest "patch" version of R , as found at att.com .