Confidentiality isn't your only concern. You should also be worried about integrity and availability. From "On The Security of Password Manager Database Formats":

  Unfortunately, [KDBX4] introduces new vulnerabilities.
  Similarly to KDB, the main problem of this format is
  the lack of authentication of *hdr*. As such, is it
  susceptible to modifications... This modification is
  not detectable by the password manager... if a user
  alters, and then saves, a corrupted database, all
  passwords previously affected by the attack are lost
  forever.

  This attack highlights a remarkable design flaw. Even
  an accidental bit-flip in the *pskey* field, e.g., due
  to a transmission error, cannot be detected, and leads
  to complete corruption of the database. Such
  corruption is unlikely to be immediately detected by
  users, who may subsequently add new entries. Over time,
  the database will be composed of both correct and
  corrupted entries, making it difficult to reconstruct
  the damaged records from a backup.

Which reminds me - I need to migrate back to Password Safe as soon as possible.