This bug has been a known issue with Captivate for some time, but it usually only affects projects that have been updated from sometime in the past where an earlier version of Captivate was used to create the original project.
The fix is relatively simple. You just need to use Save As to create a new CPTX file of your project but you need to change both the file name and the file folder location when doing the Save As. Once you have saved the file as a different name to a different folder, change the title in the publish dialog to what you want, and then publish output to that same folder to see whether the new title is now correct. If it is, then you can do another Save As to save the file back into the original folder and overwrite the previous CPTX file.
I haven't seen this happen to files created in more recent versions of Captivate. Do you know which version your project was originally created with?