I'd imagine that IB is someone with a keen sense of betrayal. The bitterness he felt for Squire, his once close friend, effectively leaving the group - & Brown - for dead, would've probably completely subsumed any anger towards Reni.
Back then, anyway. Forward wind 2 decades & with most of that bitterness gone, Reni once again became the issue. And, by the sounds of it, not just with Brown.