Played around with your nice app may be found some bugs:
"Set PWN" with Level=0 is not necessary for normal patterns working, but testing of other patterns in the app is not possible.
When i charge, testing of another pattern is less possible (interrupted earlyer?).
In the wiki there are some random mce issues mentioned, i guess it's because one of the implementations differs in the use of low-level commands, because testing is only interrupted when switching to second engine while first engine still lights (used for fading).
I am nearly sure, that "Go to Start" is only needed on one engine to repeat!