"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.