Android Built-in Email Client - Attachments won't download via Syncroton

[Carpenter, Troy]

I believe this has been discussed before, but I'm not finding anything 
in my quick searches on list or in Kolab BZ.

I have a user with a Samsung S5, using Lollipop (not sure which 
version).  With the built-in email program connected via ActiveSync 
(Syncroton), the user cannot view attachments on his phone.  I have 
replicated it on my Note Edge running 5.1.1.  I sent myself an email 
with a PDF attachment.  When using the built-in email program, if I 
select "preview" or "download" on the attachment, I get an error message 
on the phone that says "Unable to connect to server".  I remember seeing 
this in the past, but since I don't use the built-in email client on 
Android, I haven't bothered looking into it, and I guess the users have 
just lived with it until I got a call today.

In the kolab-syncroton console log, it looks like the attachment gets 
sent:

[19-Nov-2015 11:43:35,000000 -0500]: [DEBUG] 
Syncroton_Server::_handlePost::176 xml response(0):
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE AirSync PUBLIC "-//AIRSYNC//DTD AirSync//EN" 
"http://www.microsoft.com/">
<ItemOperations xmlns="uri:ItemOperations" 
xmlns:Syncroton="uri:Syncroton" xmlns:AirSyncBase="uri:AirSyncBase" 
xmlns:AirSync="uri:AirSync" xmlns:Search="uri:Search">
   <Status>1</Status>
   <Response>
     <Fetch>
       <Status>1</Status>
       
<AirSyncBase:FileReference>38b950ebd62cd9a66929c89615d0fc04::3844::2</AirSyncBase:FileReference>
       <Properties>
         <AirSyncBase:ContentType 
xmlns="uri:AirSyncBase">application/pdf</AirSyncBase:ContentType>
         <Data> [LOTS OF DATA HERE] </Data>
       </Properties>
     </Fetch>
   </Response>
</ItemOperations>

I don't see anything in the error log.  I also don't see any logs 
related to this in the Apache ssl access or error log.

Since I personally use Nine instead of the built-in Android client and 
it doesn't have the problem.  However, the logs generated look exactly 
the same.  Clearly the problem is with the Android email client, whether 
in the client itself or in how Syncroton reacts to it.

I need some help tracking down exactly what's happening, including 
increasing logs and such.  While I don't mind suggesting Nine as a 
replacement to the user, that isn't really a solution.

If the is a BZ on this already, please let me know.  The closest I saw 
is 3048, but I don't see those log signatures in my apache log.

Thanks,
Troy Carpenter
troy at carpenter dot cx