I believe it may have something to do with the settings of the sever on which the theme is hosted.
I say this, because one morning I woke up really early at 3 am an did some posting, and this error did NOT occur. Then I did some more posting at 6 am, when I had about 6 readers at the site, and IT DID REOCCUR.
So it seems to have something to do with how busy the server is. Somehow the server never gets the command to resend back the post.php file with the updated version.
For me, however, my server does save the version I just edited, both with a save as draft and save as pending.
The funny thing is, that when I publish a post, whether the server is busy or not, this problem does NOT occur.
So if we can examine the differences in scripts between saving as draft/saving as pending AND that for publishing, we might find something.
I tried changing the PHP setting on my server to allow a script to use 64M of memory, (it had been 32M), but this did not solve the problem.
And I do not believe the php.ini settings for time outs are the problem either, because the blank page occurs immediately, and my tiime outs are set to 30 and 60 seconds respectively.