Kudos for coming up with that! A great example showing that if you want the finest possible splitting of hairs you can’t go wrong if you combine religion and grammar. Let us have a look at the Hail Mary in the original Latin:
Benedicta tu in mulieribus,
et benedictus fructus ventris tui, Iesus.
And the German translation of the Western Church, the Catholic Church and the Anglican Church (the Eastern Orthodox Church is different) reads:
Du bist gebenedeit unter den Frauen,
und gebenedeit ist die Frucht deines Leibes, Jesus.
Wikipedia writes: In this context, the word “gebenedeit” (from the infinitive “benedeien”) is the Germanized form of the Latin participle “benedictus” (German: “gesegnet”; from the infinitive “benedicere”). Unlike the German word “segnen,” however, “benedicere” can refer not only to God’s bestowal of a blessing upon humanity but also to the act of worship performed by an individual worshiper or the congregation. Thus, God, too, can be “gebenedeit” (worshiped, glorified). Since there is no German equivalent for “benedicere” (literally: “to speak well”) that captures both meanings, this Germanized form is often used in place of a translation.
I guess that this germanization of the original Latin for the purposes of this prayer and only this prayer is the reason this verb does not adhere to the rule.
This has been very interesting. My colleague would not have known the Lord’s prayer of course. And even there I wonder whether there is at least a secondary stress on the first syllable. The bottom line is that while native German speakers may (and doubtless do) know the rule implicitly, they cannot state it explicitly. At least until now.
As for the sein/haben rule for the compounding verb, that seems to be a rule that is nearly ubiquitous in Indo-European languages. You can even find it in older versions of English, but it has disappeared in the modern language. But while native speakers may not know it explicitly, language teachers certainly do. But my colleague seems to have discovered something not known explicitly to anyone.