The min qty was designed to work per one customer order line.  The Application is not designed to work with multiple customer order lines, even if the sales part is the same on the lines.  It is one of these issues that some IFS customers would like it to include 1 lines only, and other IFS customers would like to it to include all customer order lines (with the same sales part).  So IFS try’s to please the majority of our customer.  Please let me know if this answers your question. 

I’d imagine this is a technical challenge, too. Right now, all the lookups are for THAT line. To implement totaling across all the lines to find the quantity for that part number would be a paradigm shift of doing look-backs at other order lines on the order. You’d also have to update any previous lines based on the new total quantity.

A custom event might be the work-around here, but a trigger can’t see other records in its own table, so a background job will be required. That makes timing and user expectations difficult to manage. (“What do you mean the record has been edited by another user? I just saved it!”)