I dragged one of my local email folder to my IMAP folder (I decided that I want to have it in IMAP, not locally any longer). This blocked the kontact's IMAP folders (greyed out), and I restarted akonadi in a meantime (typical way to workaround the problems with akonadi when changing a network connections, already reported by many people) After I started again, the local folder was already empty and the target folder (in IMAP) was empty as well. Looks like my emails documenting 3 years of work in a collaboration are lost... Reproducible: Always Steps to Reproduce: Would not even dare to repeat it again...
This has been fixed in 4.9.