[Users] Reload loses locks?

[Johan Vromans]

Claws 3.16.0 on Fedora 27.

Yesterday when I started claws-mail, and for some reason it reloaded all
mail folders (a complete IMAP fetch instead of an update fetch). 

This morning I found out that I had lost the messages that I had marked
locked.

I lock messages in a mailbox that are of special interest, so I can easily
"select all" - "delete" to clean out the mail folder while keeping the
interesting messages.

Questions: Why the reload? The log file shows nothing, it just starts with a
huge series of IMAP fetches.
Is it intended behaviour to lose the lock status of the messages?