This issue has been encountered also in thread:
http://forum.cyberlink.com/forum/posts/list/15/9333.page#41208
Apparently, after saving i lost a couple video clips references, that have been replaced by a black clip named "0,0,0".
By examining the project file (kudos to CyberLink for using XML and not binary!) i found that the missing files are defined somewhere and given an ID (say 53) but where referred by the timeline, the referring tag contains the clip name but IDREF="-1". By replacing -1 with 53 and saving, the project were correctly restored.
Hope this may be useful for fixing this bug... looks like some kind of "out of bounds" error.
Umberto