Aloha all,

Answering myself.  This bug is known and was discussed several years ago: 

From: Myles English

Subject: Re: [O] babel R: should/does order of parameters matter?

Date: Tue, 29 Mar 2011 16:57:37 +0100

Apparently, ob-R wants tables to be passed to parameters that are early in the parameter list.

Also, ob-R expects all the cells in a table to be non-empty.  An empty table cell raises Cain.

Argh.

All the best,

Tom