Mine was HE6, I have no idea if that makes a difference since I haven't tested. I only ran the flight once on the low g setting, so while my failure rate is 0%, I only have one data point. I'll take a look at my scenario, run it a few times and see what I get.
EDIT: So, I tested a handful of times with 6 boosters and low g, never exploded. I tried with no boosters and did explode. I guess the dragon doesn't like the Themis flight profile. You could fly it manually, try with 6 boosters (other arrangements might work, I don't know), or add 'REENTRY 0' to the dragon in the scenario file, as per it's documentation, and then change it after you have reached orbit.