The correct course of action is to reject any of the saint's teachings, which were contrary to dogma or that have been condemned, while maintaining the discipline of the Church and recognizing their canonizations.
This is exactly the Catholic position as I understand it. Think, for instance, of saints who lived before certain dogmas were defined by the Church. Those men and women had no infallible proclamation to guide their final judgment on the matters in question. All they had was their reason, and knowledge of the Faith as they knew and understood it. So it would have been perfectly possible for them to have a misunderstanding about some truth since "nailed down" dogmatically by the Church, and yet to have been a saint, EVEN IF (I would imagine), at the time, they even publicly fought against the truth, which they mistakenly took for error at the time.
Naturally, once the Church made it's official proclamation about a matter, a person was bound to accept and adhere to that infallible position, or risk being cut off from the Church. But before those positions were defined, there was no "break" or willful error for them to be guilty of, because the truth was yet unclear. My understanding of the Church's official position is, that if the truth is not yet dogmatically defined, then it is not a sin for someone to be wrong about it.
Also, it is my understanding that some people who strongly disagreed with the churchmen or authorities in the church on certain matters, and whom may have even publicly been saying so, nevertheless died as martyrs for the faith. Well, the Church teaches that martyrs go to heaven. So that person would be a saint, even if they were mistaken about some truth not officially defined by the Church.
Also, we have cases of great SINNERS becoming great saints later in their lives. It's easy to look at these people and say, "oh, this person did THAT, so they can't possibly have been a saint," or "their conversion could not possibly have been real, if they were doing THAT before" ... Nonsense. Such saints are the shining ray of hope for every soul to have the misfortune to begin life as a great sinner, but who have the great fortune of coming to their senses and the truth later on.
The whole thing about "judging the saints" after the fact is really ridiculous. Obviously, in terms of the post "V2" saints, I'm sure the next totally traditional pope would be more than prudent to want to look into and reexamine their cases. Which is not to say even that ALL of them are phony saints. Some may be saints indeed. But when you're talking about people declared saints by the Church, back when the Church still was in it's right mind...
Who are we to judge the Bride of Christ? Who are we to question Her infallible judgments, her wisdom, her definitions? By what authority do we put ourselves on the judgment seat, not only of the whole Church as an institution, but also of individual souls, especially those proven by miracles to be with God?
These are the main questions. It is difficult to say whether a person's soul is in heaven or not. But if the Church (in her right mind) has said so, then as Catholics who trust in the Holy Ghost, and His light in the Church, we must accept Her divinely enlightened judgments.
Obviously, we cannot follow the saints in any errors or sins they may have been guilty of. That should go without saying. But we must remember, too, that many things were not defined dogmatically and explicitly from the beginning. If you do not have the truth, you cannot be guilty of maliciously rejecting it.