What is adherence of jurisdiction?

The principle of Adherence of Jurisdiction means that once jurisdiction is vested in the court, it is retained up to the end of the litigation.  It remains with the court until the case is finally terminated.  The exception to this is where a subsequent statute changing the jurisdiction of a court is given retroactive effect, it can divest a court of jurisdiction over cases already pending before it before the effectivity of the statute.

Example:

A was charged with an offense whose penalty was below 6 years.  The case was filed with the MTC. After trial, the MTC convicted him of an offense with a higher penalty.  A questioned the conviction, claiming that the MTC had no jurisdiction over the offense since the penalty prescribed for it was higher than 6 years.  Is A correct?

A is wrong.  Jurisdiction over the subject matter is determined by the authority of the court to impose the penalty imposable given the allegation in the information.  It is not determined by the penalty that may be meted out to the offender after trial but to the extent of the penalty which the law imposes for the crime charged in the complaint.