Hello Colin,
This is an interesting observation to me because I have a mini-cluster of 4 Parallellas (3 A101040s from the 4 supplied as Kickstarter rewards and 1 P1601-DK02 - the 4th KS reward board has real problems using the Epiphany so has been placed on other duties!).
The main access method for the mini-cluster is remote access via SSH - I have only connected a monitor to the HDMI output to check what is going on while (not) booting. All boards exhibit problems occasionally when running the matmul-16 example in that some executions never finish (the host in constantly in the busy loop waiting for the Epiphany to signal it is done). Do not think I have tried the ctimer example - I should probably give it a go some time.
Although I have not been able to verify or quantify it I have had the suspicion when running repeated matmul-16 executions that the failure rate seemed to increase the more 'things' a board was doing over the network.
Other occurrences of this problem seem to have been fixed by changing PSU but so far I have tried (with various boards and collections of boards) 3 PSUs - including running the latest arrival P1601-DK02 board from one of the adapters supplied by Adapteva with no joy.
Your post has therefore made me wonder if there is in fact more to my suspicion of network activity / Epiphany problems than mere suspicion!
Regards Ralph
ps: more on my problems can be found in this thread: viewtopic.php?f=50&t=1438