Theme change not working

I have a problem with my site, if I try changing themes, certain pages will not change with the rest of the site.
It looks like it is accepting the change, all of the theme specific options are displayed in the inspector, but when using preview or publish it is always reverted back to the original theme it was created in.

there is no custom css, javascript, prefix,header,or body on the trouble pages
any suggestions? It’s a complete mystery to me. Yes, I’ve restarted, rebooted, reinstalled, regressed to the state of a crying infant…