I am using the AccelerometerV2 example... I added a 1ms timer on TPM1C0. I am currently manually sending messages from another 1392SARD. It appears that I do not always catch messages (the example also does not use any ACK) here is my code.... Also I am not entirely sure what the LOW_POWER_WHILE gets me other than a asm "WAIT" comamnd... which i think is the problem... however if i remove it, the program NEVER recieves messages from the other SARD board...
My guess is that your application is changing the internal status of the SMAC from receive to idle at some point, and therefore, you loose a packet. Remember that the SMAC has reentrant interrupts and if the internal status is corrupted/changed it leads to packet problems.
You have to be careful in how your application interfaces with the SMAC to avoid these problems.
Another possibility is that the packets are really being lost due to interference, low power, distance, a low battery, etc. Check these out.