Hi Uwe, could you try this and let me know what shows up in *Messages*?
--8<---------------cut here---------------start------------->8---
(defun my-after-insert-environment-hook (new-env beg end)
"Hook to run after a LaTeX environment is modified."
(message "Test: %s" (symbol-name last-command))
(unless (equal last-command 'LaTeX-environment)
(when (equal new-env "equation")
(unless (save-excursion (goto-char beg)
(search-forward "\\label{" end t))
(save-excursion
(goto-char beg)
(forward-line 1)
(open-line 1)
(reftex-label)
(LaTeX-indent-line))))
(when (equal (substring new-env -1) "*")
(save-restriction
(narrow-to-region beg end)
(save-excursion
(goto-char (point-min))
(LaTeX--strip-labels))))))
--8<---------------cut here---------------end--------------->8---
