Thank you for your comments.I have identified that the issue is caused by the Genus head typing animation. Quistessa is correct that it does not appear to have a resting animation, so appears to select last one used, although I have not completed debugging. Thank you for the reference to "Developer > Avatar > Animation", Lucia, That is most useful to know. I did look but had not spent a lot of time on it before I realised I had the typing animation on. Switching it off solved my problem and as this is a gift head, I can't really complain.
Thanks again