files in "cur" and "new"

Hi

I am using a freshly created mail database on a new user.  its downloaded 
emails quite happily which i've now either read or used "mark all messages as 
read" to mark the older ones.

I presume this should move all emails in "new" to "cur" within the local 
folder once they are read but its not always happening, i still have loads of 
emails in "new" in some folders. 

I could not find any bug report about this for kmail2 - is it a bug ?  I will 
log it if someone can confirm this is not how maildir should work.

regards

Ian
-- 
opensuse:tumbleweed:20170201
Qt: 5.7.1
KDE Frameworks: 5.30.0
KDE Plasma: 5.9.0
kwin5-5.9.0-1.1.x86_64
kmail2 5.4.1
Kernel:  4.9.6-1-default
Nouveau:  1.0.13_2.2