Hi Neil,
Thanks for the bug report. I've just fixed this in my copy. Unfortunately I can't get the fix into your hands until after the next release of mojoPortal which should be around April 10 or 11. There are some other changes in Site Membership Pro that depend on some new helper methods in mojoPortal that are coming in the new release, otherwise I could go ahead and package up a new release of Site Membership Pro with this fix. I will release the update for Site Membership Pro the same days as the new release of mojoPortal. Sorry for the inconvenience of the delay. If this puts you in a major bind I could possibly produce a new build of mojoPortal and of SMP just for you, to get you fixed sooner.
Thanks,
Joe