A logically asserted fact depends only on rule/facts responsible for its inital assertion, and not on rules/facts that would also have logically asserted it

Refer to forum reference for discussion leading to this JIRA.
Basically, if A => B becomes true (A is asserted) then B is logically asserted. If C => B becomes true (C is asserted) then B is logically asserted (but nothing happens as has already been asserted before. Still, logical dependencies of B change.) If A => B becomes false (A is retracted) then B should not be retracted (WHICH IT IS), because its still true due to C => B being still true. Only when C is also retracted, so neither A => B nor C => B is true, then B becomes false and should be retracted. JESS behaves that way.
Probably a special case is if B => B is also true (Jess also supports that), where B should still remain even if A and C would be retracted in the above example.

Don't know about LEAPS.