This happens to me. I highlight the clip in the timeline, go up to the viewer and change the time in the viewer window at the top left. Make it any length you want. Then go back to the timeline and you can stretch out the title crawl clip. Always thought it was a boris quirk.
Also, if the title crawl is very long, you can split the clip into two titles which is more manageable. Sometimes if I am editing in native XDCAM the title will scroll backwards if it is too long. YOu can overlap the clips in the timeline so the break between the two is unoticeable.