Just thought I'd mention that Cygnal did finally respond to my query to them on this issue (hopefully they are recovering from their move into new buildings following their acquisition by Silicon Laboratories).

In brief, the single-instruction deferral of interrupt servicing that occurs after IE or IP are written to (or RETI is executed) also occurs for the EI<E,P><1,2> registers; the full response is at:

http://www.cygnal.org/ubb/Forum1/HTML/000759.html

David