[Oberon] UIDL in POP3

[Easthope]

Folk,

Here is a small question about the Oberon MUA.

My Oberon.Text specifies "LeaveOnServer = No".
In the Local Settings mail panel, The "Leave 
messages on server" box is not checked.  Yet 
when mail is being retrieved, these lines appear 
in the System.Log.

SND: UIDL
RCV: +OK uidl command accepted.

Q.: Why does the Oberon MUA issue the UIDL
when messages are to be deleted from the server?
Why not just collect all the messages, delete 
all from the server and ignore UID?

Thanks,            ... Peter E.