But, wouldn't it be grounds for a cessation, since I've been using foreign passport which is not Canadian one, but the one from my home country, hence the grounds for the case against me ?
Obtaining Canadian citizenship technically resulted in the cessation of your status as a refugee.
Which is OK.
That is,
cessation of protected person status does NOT affect the status of a Canadian citizen.
As I previously stated, the only ground for revoking Canadian citizenship is misrepresentation. Thus, for example, if you obtained the home country passport BEFORE you became a Canadian citizen, and then in applying for citizenship you did not disclose the fact you had obtained your home country passport, that could be grounds to revoke your citizenship -- even if you did that, revocation is not likely to happen, but it would be possible.
Reviewing How the So-Called "Cessation-Clause" Works:
It may be worth reviewing how the so-called "cessation-clause" works.
Before the change in law in 2012, once a refugee became a Permanent Resident the cessation of refugee or protected person status did NOT affect that individual's status as a Canadian PR. Thus, if the refugee-PR obtained a home country passport (a prima facie ground for cessation), or traveled to the home country, or especially if the refugee-PR traveled to the home country using a home country passport, that was grounds for cessation of the individual's refugee status. But before 2012 the cessation of refugee status had NO EFFECT on PR status. It was NOT grounds for revoking or terminating PR status.
Thus, indeed, back then (before 2012) many refugee-PRs did indeed obtain a home country passport, among whom many also used that passport to travel to their home country. It seemed safe to do this because even if authorities pursued cessation proceedings, the individual remained a Canadian PR.
Then, in December 2012 Canada added the so-called "cessation-clause" to the grounds for terminating PR status. In particular, in addition to the previous provisions prescribing termination of PR status (when an individual becomes a citizen, when a Visa Office decision is made the PR failed to comply with the Residency Obligation, or when a Removal Order against the PR comes into force), in 2012 IRPA was amended to add a provision that PR status is terminated on a final decision that refugee protection has ceased (pursuant to particular provisions). This is subsection 46(1)(c.1) in IRPA.
There was rather little publicizing of this change. Not only did many of those who became a refugee-PR previous to the change continue to obtain and use home country passports, even travel to the home country, even new refugees were doing this after becoming a Canadian PR. Not only that, when it came time to apply for citizenship, refugee-PRs who typically would not have any valid passport would ask if they should obtain a passport when applying for citizenship, and not only were participants in this and other forums advising them YES, erroneously, EVEN the CIC help centre telephone agents were often telling them YES, they should obtain their home country passport before making the citizenship application. Even though just the act of obtaining a home country passport alone constituted grounds for cessation of PR status, which in turn would automatically terminate their PR status, again under subsection 46(1)(c.1) in IRPA.
Again, there was rather little publicizing of this. It became a huge and sometimes devastating pitfall for many refugee-PRs.
In 2015, more than two years after the change in law, I was reading cases involving citizenship applicants who got trapped by this. Instead of obtaining Canadian citizenship, they ran into cessation proceedings and not only failed to become citizens but lost status altogether in Canada and faced deportation. No one was talking about this. So I started this thread to WARN refugees-PRs about this pitfall. To warn refugee-PRs to NOT obtain a home country passport UNTIL AFTER they took the oath and obtained Canadian citizenship.
What made this even worse was that even though there was no prohibition or restriction against obtaining a home country passport or traveling to the home country, for those refugees who had become a Canadian PR, until the change in law in 2012, the Harper government proceeded to apply the change in law to refugee-PRs who had traveled to their home country BEFORE the change in law. This was, effectively, a retroactive application of the change in law. The injustice was blatant. The Liberal government has not rolled this back or amended the law, but now there are few refugee-PRs affected in this way. Many believe the provision is still excessively harsh, even if it is only applied to refugee-PRs for actions AFTER the change in law.
My effort here is primarily focused on helping refugee-PRs be aware of the cessation provisions so they can make decisions accordingly.
IN ANY EVENT: NO, there is NO problem lurking in the cessation provisions for a naturalized Canadian citizen who was previously a refugee-PR. 
