Sometimes CCK custom fields get lost although they appear normally in the database
Even though some fields appear correct in the DB, they don't always load up into the edit view, I've noticed similar oddness long ago when trying to replace some image assist tags in the database directly with a php script.

In our case, the edit view (node/edit) begun showing correct data after we purged all caches. 

To solve your problem, read and understand how Memcached works from http://en.wikipedia.org/wiki/Memcached -- When making manual DB edits, you must let Memcached know that you've made modifications to tables, this functionality is built into Drupal database handling, hence you'll never notice it when working directly from Drupal, but if you are making custom update queries into the tables, you must let Memcached know there was a change. Was a bit of a surprise to me since I thought it just automaticly works in the background. :)

See the example code part from the wikipedia page how to do it.

..and if you don't use custom update queries to modify those CCK fields, I suspect there must be some sort of a bug in Pressflow itself. Do the changes propagate into the edit view after few hours? Apart from this, there's not really enough info to dig in deeper :/