So I've run Trace-xDscOperation and came up with the log below.
It's start to apply the partial config....the provides a list of resources it's about to process and finally says a reboot is required. I can't work out exactly what resource is requesting the reboot.
TESTSERVER01 OPERATIONAL 23/02/2016 8:43:04 PM Starting to apply partial configuration [PartialConfiguration]MyConfig.
TESTSERVER01 OPERATIONAL 23/02/2016 8:43:04 PM Resource execution sequence :: [Registry]BlahBlah......x20 resources list here............
TESTSERVER01 OPERATIONAL 23/02/2016 8:58:55 PM WarningMessage A reboot is scheduled to progress further. Configuration will be continued after the reboot.
Also, you could try inserting some logging into the DSC config
# The message below gets written to the Microsoft-Windows-Desired State Configuration/Analytic log
Message = "Finished running the file resource with ID FW Rule File copy"
DependsOn = "[File]FWRuleFilecopy"