Hi, ianmac.
The Salutation theme doesn’t control in any way whatsoever any registration or login/logout processes, that is all handled by WordPress and, in the case of registration, the BuddyPress plugin.
If the issue goes away when you switch to using a different theme then it might be related to the Salutation theme and we will be glad to look into it. Otherwise, it’s a BuddyPress issue.