LH seems to get antsy when segments are held for any longer than a few days. You can often get an agent to extend your hold - or make a small change which will automatically do it - but I once had an agent tell me that LH was sending messages that the ticketing deadline had been passed and the LH segment was about to be cancelled even though the overall file still have validity on it. To put it in the agents words "We don't mind playing those games, but Lufthansa won't have any of it".