rosbag not publishing clock

I recorded some bagfiles with different experiments, then using the rosbag cookbook I change some timestamps (http://www.ros.org/wiki/rosbag/Cookbook). Now when playing back the new bagfiles, the clock is not being publish. I've already set the use_sim_time parameter to true and playing the bagfile with --clock option. What could be wrong? EDIT: I re-run my program and remove the compression options for the bag file. When writing uncompressed bagfiles, the clock works with no problems.