Another wrinkle (support sent me to this site for help 
)
I moved the Pre-Processing BPM to PreUpdate, since this is the first step in the tracing.
When I do everything correctly (meaning the BPM fires, but doesn’t stop) I get the following weirdness:
I enter the 4 serial numbers:
I save the receipt:
Here is what the serial number selection looks like now:
I’m just unsure if I should call this an Epicor bug? They seem to be telling me it’s outside of support since it’s a BPM. I’m only reading from the BO datasets, doing a linq query, and then comparing the totals. If it’s off it throws a flag. I’m not changing any data, and yet a serial number record disappears out of the dataset.
I’m going to play around with the BPM and see if I can pinpoint what is causing the issue. Maybe that will shed some more light on what my options are.