If you take the UPCa jasper demo , and try to increase the size of the barcodes
using "module widths", it seems the size calculation for the "pre" and post digits is not correct & they get truncated.
so take a standard UPCA code make a barcode with it .
Then change the module widths & the digests are missing, making it impossible for a human to read the resultant code, but a scanner can.
it is in teh designer & any product that produces content from that report