Thanks for that LUK! - apologies for getting it arse over. Just that in the old prog, it wrote to a registry setting ISOWRITE_LayerBreakSectors, which held the number till the next time.
It does seem that the poster has a problem with IB suggesting different sector numbers for the LB than PgcEdit, which may be because of one or both of positioning the LB on a 32K ECC boundary (padding accordingly) and 32K IFO/BUP spacing.
Regards