Well, I didn't get around to doing anything and one time I wasn't there to press 'Update later' and it went and did it without me.
I had tried turning back up off and on to see if it would help, but uncomfortably aware that that would erase the profile, but most of the data was still on the old palm on on 3rd party synergy services, so I crossed my fingers while it upgraded.
Good news! it backed up, upgraded and now yahoo mail is sync'ing properly and back up works! last sync this morning at 5.30.
I'd still recommend a 'manual' back up first, but the upgrade seemed to solve everything - except downgrading my patches. Navit also stopped, but and uninstall/reinstall solves it.
Hope that helps.