W.P. Ginfo - Top Man - You were spot on! Thanks!! Issue resolved!!!
I have (last 4 w/sites) created a 'Custom Menu' (for a mobile version of the site) but I had not dug down into 'Navigation Label', or 'Navigation Attributes' in > Menus...
I saw that the Attribute field was showing a blank - so - not knowing what this field was for - I set an attribute as 'attribute'. When I looked at my site I saw that the spurious hover over behaviour 'Home' had changed to 'Attribute', so then I went back to delete this, and the site was fine - goodbye to the unwanted hover over 'Home'.
What I cannot fathom - and probably never will - is - as a seasoned WP + twenty ten template user, is why - for the first time ever - I have seen this spurious hover over behaviour? Is this a bug in twentyten 1.5? Strange indeed. (But another lesson learned)!resolved).