"Exception: stack level too deep" on collection.clear?

Without getting too deep into my app I'm wondering if anyone has any clues what might give rise to the error posted below. It occurs when I run my unit tests.

class Actor < AR:Base   belongs_to :court_case end

class CaseCause < AR:Base   belongs_to :court_case end

class CourtCase < AR:Base   has_many :actors   has_many :case_causes   ... end

def my_test_method   ... kase.actors.clear end

def my_other_method   ... kase.case_causes.clear end

Also, Actor and CaseCause both have observers on them that attempt to update CourtCase.