The DT team has just blogged about this:
I don’t think this can be emphasised enough. The current OS betas are flakey (more so than in my own previous experience going back to OSX Lion and IOS 5). This goes double for anything using iCloud for storage and sync - it is currently extremely unreliable right now and risks losing data
Please, please make sure you have backups of your data. If you do want to play with the betas, use a separate setup.
Finally, if there are issues between the DT beta and Apple betas, don’t expect the DT team to fix them before the Apple OS release - Apple betas are moving targets.