Why doesn't mtCytB have a stop codon?

[Azur]

I was annotating mitochondrial genomes, and it dawned on me that all the mitochondrial protein coding genes except CytB have a terminal stop codon. Cytochrome b instead ends on a lone T, and the TAA stop codon is completed by the addition of 3' A residues to the mRNA.

But why? Why is CytB different?

[Endy0816]

I was reading it can cleave off the following tRNA.

Some people do have a mutant form with a stop codon causing excercise exhaustion.