We encountered the following problem:
Every time a BP group was re-saved in the dashboard, a new, empty forum with an identical name was automatically created and associated with the group. Users going to the group would only find an empty forum. It was possible to delete the new forum and re-associate the initial forum with the group, so no content was lost.
After turning off all other plugin, we found that the problem was gone. Turning plugins back on one by one, revealed that Popup Pro was at fault. We had to turn the plugin off, but hope that this bug can be fixed so that we can use it again in the future.