I have said this before on another Forum and a few did not believe me. MDF does not glue well onto the end grain. The end grain surface is too loose and too dusty to allow the glue to adhere well and permanently. Inserting a corner fillet glued and screwed into both adjacent panels restores strength to the joint but is not in the ideal position to minimise vibration. Double corner fillets is a laborious solution to this.
