Hi Simon,
I can not see any problem with properties and profile file. So its really very strange. Could you check to which host name it is resolving to in /usr/sap/<SID>/<Instance>/SMDAgent/log/SMDSystem.X.log and /usr/sap/<SID>/<Instance>/SMDAgent/log/smdagent_trace.X.trc files.
Do you see some error there?
Thanks and Regards
Sachin Gupta