Feast of the Nativity of Mary - taking the cloak off the prayer?

In a few days we will observe the Feast of the Nativity of Mary. In searching the internet for a prayer for the occasion, we found a nice one:

Vouchsafe that I may praise thee, O sacred Virgin; 
give me strength against thine enemies, 
and against the enemy of the whole human race. 
Give me strength humbly to pray to thee. 
Give me strength to praise thee in prayer with all my powers, 
through the merits of thy most sacred nativity, 
which for the entire Christian world was a birth of joy, 
the hope and solace of its life. 

When thou wast born, 
O most holy Virgin, 
then was the world made light. 

Happy is thy stock, holy thy root, 
and blessed thy fruit, 
for thou alone as a virgin, 
filled with the Holy Spirit, 
didst merit to conceive thy God, 
as a virgin to bear Thy God, 
as a virgin to bring Him forth, 
and after His birth to remain a virgin. 

Have mercy therefore upon me a sinner, 
and give me aid, O Lady, 
so that just as thy nativity, 
glorious from the seed of Abraham, 
sprung from the tribe of Juda, 
illustrious from the stock of David, 
didst announce joy to the entire world, 
so may it fill me with true joy 
and cleanse me from every sin. 

Pray for me, O Virgin most prudent, 
that the gladsome joys of thy most helpful nativity 
may put a cloak over all my sins. 

O holy Mother of God, 
flowering as the lily, 
pray to thy sweet Son for me, 
a wretched sinner.

Amen. 

This prayer is on a number of sites, Catholic and non-Catholic, either unattributed or attributed to either St Anselm of Canterbury or St Ambrose. Catholic sites range from Fisheaters to Communion and Liberation.

The opening line, "Vouchsafe that I may praise thee, O Sacred Virgin" is the first line from the Ave Regina Caelorum but not the rest of it. A cursory internet search does not find this prayer (or any portion of it) in the works of Anselm or Ambrose.

In point of fact, I don't find this prayer prior to 2010.

So why was I looking? Well, it is because this prayer contains a phrase which caused my proddy-sense to tingle; that phrase is "put a cloak over all my sins." - say what? does that not seem more appropriate for Martin Luther? This prayer also shows up primarily off the mainstream Catholic path.

Given that I failed to find any connection of this prayer with the purported source(s) or even anything of antiquity, I began to wonder if this prayer is akin to the so-called "Prayer of St Francis" - you know, the Make me a channel of your peace one that is so popular and usually attributed to St Frances even though it was first written during World War I. St Francis; not only the stigmata, but time travel! He's so cool.

Anyway, I did think of another search; instead of starting with this prayer and looking back, why not look back and see what was the prayer for the Nativity of Mary.

Bingo!

The Raccolta, replaced in 1968 by the Enchridion Indulgentiarum, contained the prayers that carry indulgences - remember indulgences? The remission of the temporal punishment for sin that has been already forgiven? uh-huh, of course.

Well, it turns out there is (oops) were a number of indulgenced prayers for Marian feasts (including her Nativity). This one is just a little different than what appears above.

Has a cloak over tradition been surreptitiously introduced? If anyone can point to a source in Anselm or Ambrose or otherwise in tradition for the first prayer, I'll put my suspicions to rest.

For now, here's a sweet one, formerly indulgenced, for not only the Marian feasts, but for all days:

Heart of Mary, Mother of God, our Mother, Heart most amiable, on which the Adorable Trinity ever looks with complacency, worthy of all the veneration and tenderness of angels and of men; Heart most like the Heart of Jesus, whose most perfect image thou art; heart full of goodness, ever compassionate towards our miseries, - vouchsafe to thaw our icy hearts, that they may be changed entirely to the likeness of the heart of Jesus. Infuse into them the love of thy virtues, inflame them with that blessed fire with which thou dost ever burn. In thee let the Holy Church find safe shelter; protect it, and be its sweet asylum, its tower of strength, impregnable against every inroad of its enemies. Be thou the road leading to Jesus; be thou the channel whereby we receive all graces needful for our salvation. Be thou our help in need, our comfort in trouble, our strength in temptation, our refuge in persecution, our aid in all dangers; but especially in the last struggle of our life, at the moment of our death, when all hell will be unchained against us to snatch away our souls, -  in that dread moment, that hour so terrible, whereon our eternity depends, and, yes, most tender Virgin, do thou then make us feel how great is the sweetness of thy motherly Heart, and the strength of thy power with the Heart of Jesus, by opening for us a safe refuge in the very fount of mercy itself, whereby we too may one day join with thee in Paradise in praising that same Heart of Jesus for ever and for ever. Amen.