Hi Stefan!
I tried you solution and it works perfectly! Just make sure to save the keymap after the call to "(run-hooks 'isearch-mode-hook)", as this is where packages like "folding" installs its keymap.
Juri and Stefan:
While looking around the isearch code, I came up with a theory why multi-buffer search in change-log-mode no longer works. isearch adds its hook to the LOCAL pre-command-hook. As change-log-mode search change buffer and the hook is not installed in the new buffer, the user can't exit isearch.
Sincerely,
Anders Lindgren