the previous verzion (1.9.2 )of the Jetpack From wordpress.com ( Automatic) - conflicted and the latest version ( 2.0.0 ) of the Jetpack also have conflict problem with 404 redirect plugin.
When user clicked on sharing buttons -opened a new window, for load the sharing providers page ( eg: facebook, twitter ), BUT - the 404 redict plugin doesnt aloved to do that --instead the new windo content redirected to the homepage - so the sharing isnt was avalaibel.
I take off the tick from the "automatic redirect" options from these 3 options:
Create automatic redirects for categories: HERE
Create automatic redirects for tags: HERE
Force current permalinks: HERE
Creates auto redirects for any url resolving to a post/page that doesn't match the current permalinks"
And now works perfect ! - please check - what would cause the conflict - I would use again the automatic redict options.