lol
OK, in true "IT Crowd" style, I thought I'd try the obvious.
Closed TC.
Closed Chrome.
Restarted TC.
Restarted Chrome.
Tried mapping the same object that kept attaching itself to my "global" page and it went straight to the new page. As it should have done all along.
I have noticed it does odd things sometimes. Earlier it was seeing nothing below except the "Sys.Browser("chrome").BrowserWindow(0).Window("Chrome_RenderWidgetHostHWND", "Chrome Legacy Window", 1)" object for Chrome. Closed Chrome and restarted it and all OK.
And sometimes it loses the codecomplete for my Script Extension methods. Go in and "Reload" script extensions and they come back.
Minor glitches I guess. Not sure if it was TC or Chrome that was glitching in this case but either way, a restart seems to have cured it.
Case closed ....