I had a few people be able to register and pay via paypal, but none of the custom fields were recorded or sent via email. The info must have been there because they paid the correct amount. By coincidence I was changing some stuff just now and I filled out a test registration and went to step 2. I got busy doing something else for about 30 mins or so. When I got back, I refreshed the page (because I was adding some styling to that page) and all of the custom field data was missing.
I think what was happening to my users was they were waiting too long on step 2 and for some reason the system let's go of their info for custom fields. I don't know how or why, but it happened. I'll post some screenshots if I can.
Not a glitch... something like that would be tied to settings on your site/server. Try adjusting the length of your session times. DT Register itself does not remove any data after a set amount of time.