Sorry for the long delay (holiday-caused, as said on mailing list) - I believe I've used the latest sources. I'll try again with 2.4 rc.
Has the entry completely disappeared? Or has it just been sorted by date into the stream of articles? I've changed dates without a problem.
Please try by tagging the article with a unique tag and see if that tag leads you to the article from the tag cloud.
Can you reproduce this behaviour from a new 2.4rc installation or from an updated older one?
Sorry, the only way I could reproduce it was by setting the date back to the past so that the entry appeared after some other entries (i.e. in chronological order) which would be as designed.
Another idea might be to check the permissions of the user running tomcat in the pebble data directory (i.e. by default ~/pebble) and its subdirectories.
Is the case catched where the entered date is back in the past? I'm asking, because no matter what the dumb user enters, the application must not crash. Instead an error message when entering the date has to occur.
You said the entry would disappear, not that the application would crash (I guess that means stacktrace to the user?). Either way: The only thing I was able to reproduce was the (possibly) changed order. If there was any user visible malfunction other than reordering, please specify and reopen.