Actually, no. According to the user manual, reads from the WRCSR register must be done as 8-bit reads. Even the Linux code does this. (I had to create the "WRCSR_R" macro myself - since the .h files from Renesas do not provide an 8-bit interface to that register).
Nevertheless, it looks like my new code is working just fine - so I'm off to my next (unrelated) problem.
Thanks!