What kind of media?
This problem occurs after mini DV tapes have been loaded in. It has happened with both my older panasonic AG-DVC30 and my newer AG DVX100.
It is really annoying because I count on using those time stamps to coordinate the addition to the clips into the editor.
It seems that I've lost some of the time stamps after they have all been loaded in. Like when I start up Premiere Pro CS4 a second time on the, the next day, I find even more of the time stamps missing, over in the project pane. I probably should carefully document that to be sure. Could be significant in the troubleshooting process.
That is strange. I've not yet seen this problem on my system. Nor do I recall it being reported by others here in the forum. I afraid I'm at a loss as to what might cause that.
A potential work around is to use Bridge before import into Premiere, renaming the clips sequentially. That way, even if the timecode disappears, the file name itself will tell you the proper order.
When the program crashes and one has to go to the auto save folder in order to pick up the most recent edits the media start and end times are not always saved.