That's not a bug. As an unsanctioned Psyker, Idira has a 5% to trigger phenomena/perils at any point she uses her powers, even if the veil is totally stable. It's perfectly possible for her to explode into a daemon at 0 veil with no warning, and it seems to be the intended behaviour. Heinrix never does this, being actually sanctioned, and neither does your PC, also being sanctioned.