I'm pretty sure the "rebaptising" they were refering to was because they didn't accept "infant baptism" as valid. If it was merely a hedge against baptism by an "invalid" priest being invalid... then I don't think it would be quite as interesting.
If it was merely a hedge against baptism by an "invalid" priest being invalid... then I don't think it would be quite as interesting. OK, quick, find the priest who baptised you and find out if he's been living a good life or a sinful one. This investigation will tell you whether you are actually validly baptised or not.
The Donatist position is one designed, apparently, to introduce doubt into the entire sacramental priesthood.
SD