When attempting to access any smb share, dolphin says that access is denied to that share, without prompting for any login or password. Reproducible: Always
Can confirm the same behavior. Dialog for login and password is never shown. For new shares it tries to login as anonymous. It logins ok if share does not require authentication, or if kio manages to pull login and pass from cache, or if you specify login and pass in cleartext in share URL.
Can't reproduce with KIO from KDE Frameworks 5. I'm happily browsing Samba shares.