Man, multiple people were ready to "go in on" Calvin which really wasn't what I intended. I was recently drafting a little ten part quick and dirty comparison of Christian denominational views on the most important/relevant theological concepts and reading about the Old Lutherans in this post really made me think about how seriously they took these things because they were literally true to them. It is either an admirable or a terrifying thing depending on your perspective.

To answer your question as well as I can from their perspective, the reformed understanding of pneumatic presence vs their understanding of the sacramental union and being forced to participate in the eucharist in that heretical way, would quite literally be grounds for leaving the continent.