Anastasios,
I am not saying this is "heretical" ect. It is in general just very wrong practice, which I believe a priest or bishop should generally be first instructed, censored, up to and including being deposed for (depending on the gravity). But if he is not, I am not going to say he is not a priest because of an error in practice.
On the other hand, I will even say that if a priest or a bishop well known for his holiness decides something different, then one should try to understand the reasonings. He is after all considered to know better, and some things are not always completly black and white.
To reinforce the general idea thought, and it sounds like you agree...
You know Anastasios that the only difference between a deacon, a priest, a bishop, and a layman, is the difference in Charismata. They are all members of the Church.
So if baptized Christians should only be in the altar out of nessesity, and even catechumans have to leave the liturgy when the words are spoken "catchumans depart" (and I know you probably disagree with this practice), and if the "secret prayers" are not to be heard and the altar area not even seen by the layman during this time, what does this say about heretic "bishops" being in the altar area!? Are they not even less privelged than a catechuman? By letting them in the altar, does that not say to faithful these men are worthy, giving legitimacy to their errors and separation from the Church?
Now I could start citing all the examples of the Saints who would not even share a bathhouse with a heretic "bishop", but I think it is abundantly clear what the Church teaches regarding this. And I think you agree Anastasios. It is your willingness to agree when your conscience tells you to that shows an honesty, and leads me to think you'll join the church one day, God willing.
But those minimalists who are constantly struggling to dissect, surgically remove, and hold up high examples of error are fighting Christ and His Church, they are "kicking against the goads".