I can't find the desired information and must conclude that I may have confused +Photios with someone else (perhaps Celarius). I also don't have a transcript of the council of 890 which restored +Photios. The sources seem to concentrate only on the council of 880, which deposed him, and which the RCC, in a reversal, recognizes as the "Eight Ecumenical Council."
My memory probably misleads me, then, since I "remember" reading the text of +Photos's charges and was under the impression that one of the issues was unleavened bread used by the Latins. I can't think of why I would have thought that if I hadn't seen it. On the other hand, I never read Pat. Celarious's addition of azyme controversy on the list of Catholic heresies while emitting the filioque, which I discovered during this search.
As for Pope Leo III and the filioque, this is a matter of interpretation. John Romanides insists that he agreed to it theologically out of concern that Franks could be upset, but that his insistance on the Fathers and the Councils was a diplomatic way of saying otherwise.
Others interpret it straight forward: the Pope allowed filioque to be sung but not included in writing. Curiously, Encyclopedia Britannica seems to have it backwards.
"Yet in 809, when approached by Charlemagne's theologians, Leo confirmed the dogmatic correctness of the Filioque clause (the doctrine that the Holy Spirit proceeds from both the Father and the Son) introduced into the Nicene Creed; but, because that clause had always been rejected by the Eastern churches, Leo, in the interest of peace with the Greeks, urged that the creed should not be chanted in the public liturgy." (Encylcopedia Britannica)
"[Pope] Leo [III] accepts the teaching of the Fathers, quoted by the Franks, that the Holy Spirit proceeds from the Father and the Son, as taught by Augustine and Ambrose. However, the Filioque must not be added to the Creed as was done by the Franks, who got permission to sing the Creed from Leo but not to add to the Creed. (John S. Romanides)
I think that Romanides' reference is that Leo consented to the Franks' desire to sing the Creed in the Liturgy *at all.*
The addition of saying or singing the Creed during the Divine Liturgy is a relatively late addition. Its ancient use was in baptismal services.
At least that is how I read Romanides -- Leo gave permission to sing the Creed in the Liturgy, but insisted that it be in its original form. I may be wrong, but I can't make it make sense otherwise.