Messages are lost when client connection closes unexpected

Scenario:

Openfire is configured to store offline messages

1. Connected XMPP client loses it's connectivity (Airplaine mode on a smartphone, etc.)
2. Send a message to the client, which still shows up as online
3. After 5 minutes (I think this is the default client connection timeout) the client goes in offline state
4. Client reestablishes the XMPP connection somehow and does an offline message retrival
5. The Message send in 2. is not part of the cached offline messages.

It would be nice if openfire would put the message from 2. in the offline messages pool for the client. Therefore I'd like to make a future request. Or is this already implemented somehow? Then what's needed to make it work as one would expect it.

Can someone point me to the source code part that is responsible for incoming client messages?

Flow