Webtop display duplicates

On a fresh install (this week - latest version) I am seeing occasional duplicate emails displayed in Webtop Inbox.

The duplicates are definitely not in the VMail folder, nor visible in other clients (eg Outlook, Roundcube etc).

Does Webtop just read/display the users VMAIL folder directly or does it pull that data into a database first? That may help me locate the glitch.