Currently, it appears that the AutoResponder rules are exported on the UI thread (i.e. when exporting a massive Fiddler AutoResponder rule set, Fiddler is "Not responding..."
With a large AutoResponder set, Fiddler's UI may become unresponsive for minutes.
I believe this also prevents incoming connections from being processed - if true, that is even worse.
If this does get done on a background thread, to keep consistency, perhaps the AutoResponder rules window should be "disabled" (greyed out) so no changes can be made to the rules while exporting.