Oh, it's easy. Church discipline is NEVER dogmatic.
But it is certainly protected from error. Read these quotes carefully and ponder the implications involved:
P. Hermann (1908)
"The Church is infallible in her general discipline. By the term general discipline is understood the laws and practices which belong to the external ordering of the whole Church. Such things would be those which concern either external worship, such as liturgy and rubrics, or the administration of the sacraments, such as Communion under one species....
The Church in her general discipline, however, is said to be infallible in this sense: that nothing can be found in her disciplinary laws which is against the faith or good morals, or which can tend [vergere] either to the detriment of the Church or to the harm of the faithful.
That the Church is infallible in her discipline follows from her very mission. The Church's mission is to preserve the integral faith and to lead people to salvation by teaching them to preserve whatever Christ commanded. But if she were able to prescribe or command or tolerate in her discipline something against faith or morals, or something which tended to the detriment of the Church or to the harm of the faithful, the Church would turn away from her divine mission, which would be impossible."
Institutiones Theologiae Dogmaticae. 4th ed. Rome: Della Pace 1908. 1:258.
A Dorsch (1928)
"The Church is also rightfully held to be infallible in her disciplinary decrees....
By disciplinary decrees are understood all those things which pertain to the ruling of the Church,, insofar as it is distinguished from the magisterium. Referred to here, then, are ecclesiastical laws which the Church laid down for the Universal Church in order to regulate divine worship or to direct the Christian life."
Institutiones Theologiae Fundamentalis. Innsbruck: Rauch 1928. 2:409.
R.M. Schultes (1931)
"The infallibility of the Church in Enacting Disciplinary Laws. Disciplinary laws are defined as 'ecclesiastical laws laid down to direct Christian life and worship'.....
The question of whether the Church is infallible in establishing a disciplinary law concerns the substance of universal disciplinary laws - that is, whether such laws can be contrary to a teaching of faith or morals, and so work to the spiritual harm of the faithful....
Thesis. The Church, in establishing universal laws, is infallible as regards their substance.
The Church is infallible in matters of faith and morals. Through disciplinary laws, the Church teaches about matters of faith and morals, not doctrinally or theoretically, put practically and effectively. A disciplinary law therefore involves a doctrinal judgement....
The reason, therefore, and foundation for the Church's infallibility in her general discipline is the intimate connection between truths of faith or morals and disciplinary laws.
The principal matter of disciplinary laws is as follows: a) worship...."
De Ecclesia Catholica. Paris: Lethielleux 1931. 314-7.
Valentino Zubizarreta (1948)
" Corollary II. In establishing disciplinary laws for the universal Church, the Church is likewise infallible, in such a way that she would never legislate something which would contradict true faith or good morals.
Church discipline is defined as 'that legislation or collection of laws which direct men how to worship God rightly and how to live a good Christian life.'....
Proof of the Corollary. It has been shown above that the Church enjoys infallibility in those things which concern faith and morals, or which are necessarily required for their preservation. Disciplinary laws, prescribed for the universal Church in order to worship God and rightly promote a good Christian life, are implicitly revealed in matters of morals, and are necessary to preserve faith and good morals. Therefore, the Corollary is proved."
Theologia Dogmatico-Scholastica. 4th ed. Vitoria: El Carmen 1948. 1:486.
Serapius Iragui (1959)
"Outside those truths revealed in themselves, the object of the magisterium's infallibility includes other truths which, while not revealed, are nevertheless necessary to integrally preserve the deposit of the faith, correctly explain it, and effectively define it....
D) Disciplinary Decrees. These decrees are universal ecclesiastical laws which govern man's Christian life and divine worship. Even though the faculty of establishing laws pertains to the power of jurisdiction, nevertheless the power of the magisterium is considered in these laws under another special aspect, insofar as there must be nothing in these laws opposed to the natural or positive law. In this respect, we say that the judgement of the Church is infallible....
1o) This is required by the nature and purpose of infallibility, for the infallible Church must lead her subjects to sanctification through a correct exposition of doctrine. Indeed, if the Church in her universally binding decrees would impose false doctrine, by that very fact men would be turned away from salvation, and the very nature of the true Church would be placed in peril.
All this, however, is repugnant to the prerogative of infallibility with which Christ endowed His Church. Therefore, when the Church establishes disciplinary laws, she must be infallible."
Manuale Theologiae Dogmaticae. Madrid: Ediciones Stadium 1959. 1:436, 447.
Joachim Salaverri (1962)
"3) Regarding disciplinary decrees in general which are by their purpose [finaliter] connected with things which God has revealed.
A. The purpose of the infallible Magisterium requires infallibility for decrees of this kind....
Specifically, that the Church claims infallibility for herself in liturgical decrees is established by the law of the Councils of Constance and Trent solemnly enacted regarding Eucharistic Communion under one species.
This can also be abundantly proved from other decrees, by which the Council of Trent solemnly confirmed the rites and ceremonies used in the administration of the sacraments and the celebration of the Mass."
Sacrae Theologiae Summa. 5th ed. Madrid: BAC 1962. 1:722,723.