I'm running on kubuntu 12.04 and finally enabled the backport repository 
yesterday to upgrade to 4.9.  I'm happy to say that the search function 
appears to be working a *lot* better, problems I thought I saw in indexing 
(multiple copies of the same email in the results) is gone and more results 
are being reported.  Way cool and kudos to the developers to get this working.

The other problems I was having (inability to delete messages (they'd return 
after leaving and returning to the folder) and not being able to create new 
subfolders) was being caused by a setting in the KMail "Accounts" where the 
mail folder was set to "read only".  Resetting this seems to remove both of 
the odd behaviors and makes sense in retrospect.  I must have set that at 
sometime when I was working through some issues in earlier KMail2 versions.  

Maybe an error message or info message at the time of a manual deletion in a 
read-only mail source would help the next user to understand the cause of the 
problem?  If the read-only is inherited by all the subfolders maybe something 
in the folder properties reflecting this (perhaps a uneditable selected 
checkbox saying "readonly"? 

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