I have found a work around. I eventually found a post in the forum with Studio 23 and it suggested that the length recorded when you save a title is related to it's position on the time line.
So I called up the current projectand copied the title on the timeline that was OK then created a new movie and pasted the title in at the very start then saved the title.
If I then go back to the original project I can insert the title from the library and it is the correct 4 seconds long.
The title editor seems to taken a few steps backwards since studio 20, certainly a few bugs to sort out.