Kolab 3.3, dovecot 2.2.13, Activesync iOS Mail.app crash

[zero one]

Hi,
I have a weired problem. I am using:
- Kolab 3.3- dovecot 2.2.13
Everything works fine. 
One problem: When deleting a mail in iOS mail.app which is connected via Activesync the mail.app crashes. Happens on two iOS 8 devices each time. Nothing noticeable in the logs.
Maybe this is a known problem? 		 	   		  
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