A query in Streaming Replication

Hello,
I use streaming replication in async mode. When master gets down,
slave will be promoted using a trigger file. During this process ".partial"
file will be created and a WAL file with same ID will be created in a
different time line in slave. When master comes back as slave, it will be
synced to the current master. This is the normal procedure as far as I
understood. But in some cases, ".partial" file is not getting created and
peer DB which comes back as slave is unable to sync when this happens..
Please suggest if this happens in any scenario and how to overcome this.

Thanks & Regards:
Manoj.