MRCP 81 vs. MRCP 40

I was reading on some cases last night while working on a number of briefs I have due.  In reviewing a case a notice there appears to be some conflict with Mississippi Rule of Civil Procedure 81 and Mississippi Rule of Civil Procedure 40.  Rule 81 provides that certain matters have to be tried on a day certain or continued to another date.  However, Rule 40 provides that trials may be set by agreement.  The question then comes does Rule 81 override Rule 40 or does Rule 40 override Rule 81?  This normally comes up after both parties get an attorney and agree to set the matter for a trial later once discovery is complete.  My gut says that a trial set by agreement acts as a waiver.  However, there is an argument that Rule 81 is jurisdictional which can be attacked whenever.