Calculation Manager Rule Disappears

We are having in issue in which a particular pair of business rules keep disappearing from our plan type.  The rules are still in Calculation Manager.  The rules in question are assigned to a form that also has other rules assigned to it.  Only these two rules disappear.  They still show up on the business rules tab of the report in edit mode, but are not actually attached or even in the plan type anymore.

We do not use security on our rules, but the only way I've been able to get these rules to re-attach to the forms is to re-deploy them and then assign write access for the whole company to them.  It has happened more than once, and always with the same two rules (identical rules with the exception of one member in the FIX).