Justin,
Maybe I missed it, but I too would appreciate something a bit more explicit (yes or no?) regarding the new calendar and heresy. Was the adoption of the New Calendar, in itself, a heresy? I don't believe one can argue that it was in fact a heresy without cutting their own legs out from underneath them (especially from the position of ROAC/ROCOR, who have often times had new calendar parishes under her... and certainly we don't accept "heresy" through "economy").
The question, as OOD indicates, doesn't lend itself to a sweeping "yes or no" answer that will apply to each and every circumstance.
It is unambiguous that the motives behind the EP's move to introduce the new calendar were heretical. The 1920 Patriarchal encyclical on ecumenism (which lists the adoption of the new calendar as the first of several practical steps towards a form of unia which goes against Orthodox principles) is quite obviously heretical, so much so that I've yet to even see an attempt to redeem the document for the benefit of "scandalized" Orthodox who take exception to it. I suspect this is because it is quite plain that such is impossible.
In this sense, it was a disciplinary change in the Church's liturgical life, which was wedded to an agenda (ecumenism) whose principles are heretical. This is beside the canonical issues which make it's adoption "problematic" (various synodical/encyclical condemnations of the Gregorian calendar and it's adoption by the Orthodox, almost all of which not only had the endorsement of, but were formulated by the EP in better times.)
There is of course a difference between something being "wrong" (even heretical, as in certain teachings or propositions) and the rest of the local Churches becoming conscious of such. It seems apparent that at least for a time, while the ROCOR (and even the Patriarchate of Jerusalem and some others) voiced unhappy sentiments about this change and the violence it did to the liturgical unity of the Church, they did not thoroughly comprehend the canonical issues involved, which were much more immediate to those living in lands who were actually subjected to this change (such as in Greece and Romania.) We also cannot be too legalistic about these things - that this subject got lost in other equally urgent problems/upheavels (communist revolution and subversion of much of the "official Church" in Russia, the juristictional battles/confusion in the Americas, etc.) should also be considered.
The word "economia" in Greek refers to "rule of the house", which is why it could be alternately translated "husbandry". This is why the Church uses this to speak of God's government of the entire creation, as well as the evangelical dispensation for the salvation of souls (God's economy of salvation). While many use the term "economy" to speak solely of examples where the Church has acted leniently, willing to accept/tolerate something less than the "canonical ideal" for the sake of the salvation of sinners, strictly speaking the entire excercise of the Church's "government" and "authority".
Given this, it is within the Church's power to accept/tolerate things which go against canonical exactitude, or somehow go against the evangelical perfection proclaimed by Christ (such as the issue of divorce...though Christ Himself admitted exception even to this), if they perceive it to be the "lesser evil" in a situation or somehow advantageous for those they are ministering to.
It is on this basis, that ROCOR's leniency towards some communities it received from new-calendar churches is understandable - particularly when there was obviously no question of "heretical" motives. However, all lieniencies extended on the basis of the Church's authority (if genuine, and not simply liberal abuses) always implicitly recognize that such condescension is "against the rule".
Unto the pure all things are pure: but unto them that are defiled and unbelieving is nothing pure; but even their mind and conscience is defiled. (Titus 1:15)
This is an outgrowth of the doctrine which proceeded from the Saviour's own lips as recorded in the Holy Gospels. No calendar, no "day" or "season" can, of itself, make someone a sinner. These are all simply things, of themselves just sensual phenomena...they are neutral. The problem with the new calendar then, arises in the form of the moral dimension which the issue has associated with it - the violence done by it to the unity of the Church (by those who established it in contravention to the common mind and resolutions of the Church, which had been quite clearly stated in times past), and the heretical mindset which motivated this change in the first place.
Seraphim