After automatic reconnection, client appears connected but messages to publish keep getting buffered

- [x] Bug exists Release Version 1.1.1 ( Master Branch)
- [ ] Bug exists in Snapshot Version 1.1.2-SNAPSHOT (Develop Branch)

We're using eclipse.paho.client.mqttv3 1.1.1 and observe the following (rare) behavior :

Sometimes, after an automatic reconnection to the broker, the client appears connected anew (isConnected() returns `true`) but new messages keep getting buffered (buffer queue continue to grow until eventually service is restarted).

We monitor `isConnected`, `getBufferedMessageCount` & `getPendingDeliveryTokens` size ; you can see their behavior in such an instance :

The issue is hard to reproduce since it seems to happen only sporadically (many auto reconnections do not yield this situation).

Are there other metrics we should look for? Something specific in the logs?

Thanks in advance