For the one hack that starts trace progress, trace progress itself is not reduced by defensive hackware or hub bonuses. So a hack with 50% success chance can go to 50% trace in the first try, despite having 50%+ defensive bonuses. Every subsequent 50% hack progresses the trace by 15% (or was it 10%?).
This bug is older than Beta 7.
Right, it's always been that way since the first release. As per the effect's description, defensive hackware only protects against "tracing progress advances," not the initial state of the trace immediately on detection.