Leavened Bread in a Preface of the Old Roman Mass

A large number of variable Proper Prefaces for the Mass are used in our Orthodox Western Rite; they contain significant didactic material on various theological matters.  In the Preface for the 22nd Sunday after the Octave Day of Pentecost, which one can also find in the Sacramentary of Robert of Jumieges, we have the following: 

"Maiestatem tuam suppliciter depraecantes, ut expulsis azymis vetustatis, ilius agni cybo satiemur et poculo, qui et nostram imaginem reparavit, et suam nobis gratiam repromisit, Iesus Christus Dominus noster.  Per quem..."

(...that, suppliantly beseeching Thy Majesty: that, having thrown away the unleavened bread [azymis] of the old dispensation [vetustatis=old age, old ways, etc], we may be filled with the Food and Drink of That Lamb That hath both repaired our appearance [imaginem] and again promised us His Grace, Jesus Christ Our Lord. Through Whom...)

This is a testimony to the old leavened bread in the Mass; the azyme (unleavened bread) of the Old Testament is removed, and, in its place, leavened bread is used.