Hello.
I've started using 'sieve' utility for filtering mail which is stored in the maildir format. And I found the following issue: when 'sieve' decided to put several messages into the one box, then only one (the last processed) message was in the new/ directory, but all the other were put into the cur/ directory (however, these messages were put into the new/ directory firstly and then moved into the cur/).
Therefore I propose the solution described in the attached patch. Patched 'sieve' works fine with it.
Unfortunatelly, I'm not 100% sure that this patch will not affect all the other mailutils components which can use maildir format as a backend.