yeah - i know all about that bug.
to fix:
Edit Plugin: Thread Rate Credit Application
FIND
PHP Code:
$reward = (1 + $this->registry->userinfo['permissions']['credit_threadrate'] * $this->registry->userinfo['credits_numrefs']) * $this->registry->userinfo['permissions']['credit_threadrate'];
replace with
PHP Code:
$reward = (1 + $this->registry->userinfo['permissions']['credit_refbonus'] * $this->registry->userinfo['credits_numrefs']) * $this->registry->userinfo['permissions']['credit_threadrate'];
might want to recalc everyone's credits afterwards