>> 0. emacs -Q
 >> 1. M-x
 >> 2. C-x t 2
 >> 3. C-x o     ;; switches to the minibuffer
 >> 4. C-x t 2
 >>
 >> Debugger entered--Lisp error: (error "Specified root is not an ancestor of specified win...")
 >>    delete-other-windows-internal(#<window 4 on  *Minibuf-1*> #<window 8 on *scratch*>)
 >>    delete-other-windows()
 >>    tab-bar-new-tab-to()
 >>    tab-new(nil)
 >>    funcall-interactively(tab-new nil)
 >>    command-execute(tab-new)
 >
 > Martin, could you please help to debug this problem.
 >
 > Does the error occur because the window configuration is broken?

No.  Binding 'ignore-window-parameters' to t skips the usual error
message that you "Can't expand minibuffer to full frame".  Does the
attached patch fix it?

martin