After you publish images to Flickr, images unexpectedly return to the Modified Photos to Re-Publish section of the Publish Service in Photoshop Lightroom 3.x.
If you have a free Flickr account, republishing your image removes all comments and ratings from images that have been updated. If you have a free Flickr account, the image can remain in the Modified Photos to Re-Publish section indefinitely.
To keep images in the Modified Photos to Re-Publish section:
If you have a Pro Flickr account, images in the Modified Photos to Re-Publish section are always republished.
Many changes trigger a move to the Republish section. These changes include GPS, IPTC, keyword, and rotation changes, as well as changes to Publish Manager Settings and Develop settings.
If you haven't changed the image, and it moves to the Republish section, consider submitting an external bug report form here: https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform.