On a recent project I've noticed that if I add a new field to my dexterity based content type it sometimes disappears.
Think it may have related to load balanced ZEO clients I did a rolling restart. It still seemed to exhibit the same behaviour.
We're using TTW development more and more so this is important for my team. Adding a field and having it disappear is not confidence inspiring. Specifically adding two new fields "speaker_title" and "speaker_organization", the fields will "disappear" from the content type after a refresh.